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1? 



A COMPLETE TREATISE 



ECTRO-DEPOSITION OF METALS : 



COMPRISING 

ELECTRO-PLATING AND GALVANOPLASTIC OPERATIONS, THE DEPOSITION OF 

METALS BY THE CONTACT AND IMMERSION PROCESSES, THE COLORING OF 

METALS, LACQUERING, THE METHODS OF GRINDING AND POLISHING, 

AS WELL AS 

DESCRIPTIONS OF THE VOLTAIC CELLS, DYNAMO-ELECTRIC MACHINES. 

THERMO-PILES, AND OF THE MATERIALS AND PROCESSES 

USED IN EVERY DEPARTMENT OF THE ART. 



TRANSLATED FROM THE LATEST GERMAN EDITION OF 

DR. GEORGE LANGBEIN, 

n 

PROPRIETOR OF A MANUFACTORY FOR CHEMICAL PRODUCTS, MACHINES, APPARATUS, 

AND UTENSILS FOR ELECTRO-PLATERS AND OF AN ELECTRO-PLATING 

ESTABLISHMENT IN LEIPZIG.^ 



WITH ADDITIONS BY 
WILLIAM T. BRANNT, 

EDITOR OF THE " TECHNO-CHEMICAL RECEIPT BOOK." 

SEVENTH EDITION, REVISED AND ENLARGED. 
ILLUSTRATED BY ONE HUNDRED AND FIFTY-FIVE ENGRAVINGS. 



PHILADELPHIA : 
HENRY CAREY BAIRD & CO., 

INDUSTRIAL PUBLISHERS, BOOKSELLERS, AND IMPORTERS, 

810 Walnut Street. 

1913 






Copyright, by 

HENRY CAREY BAIRD & CO. 

1913. 



/ 



? ^\3- 



PRINTED AT THE 

WlCKERSHAM PRINTING HOUSE, 

111-117 EAST CHESTNUT STREET, 

LANCASTER, PA.. U. S. A. 



©CI.A357445 



PREFACE TO THE SEVENTH AMERICAN EDITION. 



The number of American editions through which Dr. George 
Langbein's work, Handbuch der elecktrolytischen Metall-Nieder- 
schlage, has passed in rapid succession, and the continued 
demand for it, may be accepted as evidence that the book, 
written from a scientific, as well as practical, standpoint, has 
been found to fulfill the purpose for which it is primarily 
intended, namely to serve as a ready book of reference and 
practical guide to the electroplater, who, if he would be a 
master of his art, must be conversant with the scientific prin- 
ciples upon which it rests. 

In this the seventh American edition, now presented to the 
public, the general scheme and scope of the sixth edition have 
been retained, but a thorough revision has been made, and a 
good deal of new matter has been added. 

Due attention has been paid to all important innovations, 
and it has been endeavored to include all practical methods 
of plating which have become known since the publication of 
the sixth edition, as well as the most recent machinery and 
apparatus. 

The editor is under obligations to The Hanson & Van 
Winkle Co., of Newark, N. J., the well-known manufacturers 
of, and dealers in, electroplaters' supplies and to The Egyptian 
Lacquer Manufacturing Co., of New York, for valuable in- 
formation and engravings. He has also diligently consulted 
the leading trade journals and freely quoted from them, due 
credit having been given in the text ; but he would acknowl- 
edge his special indebtedness to " The Metal Industry." 

The publishers have spared no expense in the proper il- 

(iii) 



iv PREFACE TO THE SEVENTH AMERICAN EDITION. 

lustration and the mechanical production of the work, and, 
like the previous editions, it has been provided with such a 
copious table of contents and very full index as to render 
reference to any subject prompt and easy. 

W. T. B. 

Philadelphia, October 15, 1913. 



PREFACE TO THE FIRST AMERICAN EDITION. 



The art of the electro-deposition of metals has during recent 
years attained such a high degree of development that it was 
felt that a comprehensive and complete treatise was needed to 
represent the present advanced state of this important industry. 
In furtherance of this object, a translation of Dr. George Lang- 
bein's work, Vollstdndiges Handbuch der Galvanischen Mettall- 
Niederschlage, is presented to the English-reading public with 
the full confidence that it will not only fill a useful place in 
technical literature, but will also prove a ready book of refer- 
ence and a practical guide for the workshop. In fact, it is 
especially intended for the practical workman, wherein he can 
find advice and -information regarding the treatment of the 
objects while in the bath, as well as before and after electro- 
plating. The author, Dr. George Langbein, is himself a 
master of the art, being the proprietor of an extensive electro- 
plating establishment combined with a manufactory of chem- 
ical products, machinery and apparatus used in the industry. 

The results yielded by the modern dynamo-electric ma- 
chines, to which the great advance in the electro-plating art it 
largely due, are in every respect satisfactory, and the more so 
since the need of accurate, and at the same time handy, 
measuring instruments has also been supplied. With the 
assistance of such measuring instruments, the establishment 
of fixed rules regarding the current-conditions for an electro- 
plating bath has become possible, so that good results are 
guaranteed from the start. While formerly the electro-plater 
had to determine the proper current-strength for the depositions 
in an empirical manner, by time-consuming experiments, to- 
day, by duly observing the determined conditions, and pro- 

(v) 



VI PREFACE TO THE FIRST AMERICAN EDITION. 

vided with well-working measuring instruments, he can at once 
produce beautiful and suitable deposits of the various metals. 

The data referring to these current-conditions, according to 
measurements by Dr. Langbein, are given as completely as 
possible, while for the various baths, only formulae yielding 
entirely reliable results have been selected. To most of the 
baths a brief review of their mode of action and of their ad- 
vantages for certain uses is added, thus enabling the operator 
to select the bath most suitable for his special purpose. To 
the few formula? which have not been tested, a note to that 
effect is in each case appended, and they are only given with 
due reserve. 

To render the work as useful as possible, the most suitable 
formula? for plating by contact and immersion, as well as the 
best methods for coloring the metals, and the characteristic 
properties of the chemicals used in the industry, are given. 
However, the preparation of the chemicals has been omitted, 
since they can be procured at much less expense from chemi- 
cal works than it would be possible for the electro-plater to 
make them in small quantities, even if he possessed the neces- 
sary apparatus and the required knowledge of chemistry and 
skill in experimenting. 

It is hoped that the additions made here and there by the 
translator, as well as the chapter on " Apparatus and Instru- 
ments," and that on " Useful Tables." added by him, may 
contribute to the usefulness of the treatise. 

Finally, it remains only to be stated that the publishers 
have spared no expense in the proper illustration and the 
mechanical production of the book ; and,, as is their universal 
practice, have caused it to be provided with a copious table of 
contents, and a very full index, which will add additional 
value by rendering any subject in it easy and prompt of 
reference. 

W. T. B. 

Philadelphia, July 1, 1891. 



CONTENTS. 



I. 
HISTORICAL PART. 



CHAPTER I. 
Historical Review of Electro-Metallurgy. 

PAGE 

The method of coating metals by simple immersion known to Zozimus 
and Paracelsus; Luigi Galvani's discovery, in 1789, of the electric 
contact-current; Alexander Volta's discovery, in 1799, of the true 
causes of the electric contact-current; Galvani's experiments . . 1 

Erroneous inference drawn by Galvani from his experiments; General 
ignorance in regard to the electric current; Discovery which led to 
the construction of the pile of Volta, or the voltaic pile; Cruik- 
shank's trough battery 2 

Decomposition of water by electrolysis by Nicholson and Carlyle, 
1800; Wollaston's observations, 1801; Cruikshank's investigations, 
1803; Brugnatelli's experiments in electro-gilding, 1805; Sir Hum- 
phry Davy's discovery of the metals potassium and sodium, 1807; 
Prof. Oersted's discovery of the deflection of the magnetic needle, 
1820 3 

Construction of the galvanoscope or galvanometer; Ohm's discovery, 
in 1827, of the law named after him; Faraday's discovery, in 1831, 
of electric induction; First electro-magnetic induction machine con- 
structed byPixii; Faraday's electrolytic law laid down and proved in 
1833; Production of iridescent colors, in 1826, by Novili; Production 
of the amalgams of potassium and sodium, in 1853 by Bird . . 4 

Discovery of the actual galvanoplastic process, in 1838, by Prof. 
Jacobi; Claims of priority of invention by T. Spencer, and C. J. Jor- 
dan; Labors of the Elkingtons and of De Ruolz; Murray's discov- 
ery, in 1840, of black-leading 5 

Introduction, in 1843, of gutta-percha by Dr. Montgomery; First em- 
ployment, in 1840, of alkaline cyanides by Wright; Patent for the 
deposition of nickel, 1840; Origination of the term "electro-metal- 
lurgy" by Mr. Alfred Smee, 1841; Prof. Bcettger's discovery, in 
1842, of the deposition of nickel from its double salt .... 6 

(Vii) 



Vlll CONTENTS. 

PAGE 

First deposition of metallic alloys by De Ruolz; First use of thermo- 
electricity, in 1843, by Moses Poole; Advances in the art of electro- 
deposition; First magnetic machine that deposited silver on a prac- 
tical scale constructed, in 1844, by Woolwych; Attempts, since 1854, 
by Christoffle and Co., to replace their batteries by magneto-elec- 
trical machines; The Alliance machine; Objections to Wilde's 
machine; Dr. Antonio Pacinotti's invention, in i860, of the ring 
named after him. 7 

Siemens' dynamo machine, 1866; Wheatstone's dynamo machine, 
1867; Zenobe Gramme's machine, 1871; Hefner- Alteneck's machine, 
1872; Siemens & Halske machine, 1874; S. Schuckert's machine; 
Impetus given to the electro-plating industry by the construction of 
suitable dynamo machines 8 



II. 

THEORETICAL PART. 



CHAPTER II. 
Magnetism and Electricity. 
Magnetism. 
Loadstone or magnetic iron ore; Natural and artificial magnets . . 9 
Definition of the magnetic poles; Neutral line or neutral zone; Mag- 
netic meridian; North and south poles; Phenomena of attraction and 

repulsion; Ampere's theory 10 

Magnetic field n 

Electro-Magnetism . 

Direction of the reflection of a magnetic needle; Instruments for recog- 
nizing feeble currents u 

Galvanoscopes or galvanometers; Astatic galvanometer; Instruments 
for measuring the intensity of the current by the magnitude of the 
deflection of the magnetic needle; Definition of electro-magnets . 12 

Expression of the magnitude of the magnetizing force of the current; 
Remanent or residual magnetism; Properties of an electro-magnet; 
Flow of the magnetic lines of force; Magnetic field . . . .13 

Direction and magnitude of the field-force; Effect of the electro-magnet 
upon soft iron; Definition of permeability . . . . . .14 

Magnitude of the magnetic induction; The solenoid . . . .15 

Induction. 

Definition of induction 15 

Primary, inducing or main current; Secondary, induced or induction- 
current 16 



CONTENTS. IX 

PAGE 

Direction of the induced current ........ 17 

Electro- magnetic alternating actions; Hand-rule for following the 
direction of the induced current ........ 18 

Fundamental Principles of Electro-Technics. 

Electric units 18 

Comparison of the electric current with a current of water . . . 19 
Definition of current-strength; The coulomb; The ampere; Electro- 
motive force or tension . . 

The volt; Difference of electro-motive force or difference of potential 

The volt-ampere, or watt; Unit of electrical work; Electric resistance 

Electric resistance of the current; The ohm; Law of Ohm; Equations 

Examples to equations 22 

Internal and external resistance; Decrease in electro-motive force . 23 
Proportion of the current-strength to the resistance of the current; 
Equation for calculating the decreasing electro-motive force; Im- 
pressed electro-motive force; Specific resistances . . . .24 
Specific resistances and coefficient of temperature of the metals . . 25 
Coefficient of temperature; Law of Kirchhoff; Branching or distrib- 
uting the current; Main wire and branch wires . ... . .26 

Summary of Kirchhoff 's law • - - ■ • • 2 7 

Law of Joule 28 

Frictional Electricity . 

Idio-electrics 28 

Non-electrics; Good and bad conductors; Electroscope; Kinds of elec- 
tricity .29 

Contact Electricity . 

Generation of a current of electricity by the contact of various metals; 
Potential; Difference of potential; Series of the electro-motive force 
of the metals 30 

Galvanic current or hydro-electric current; Galvanic element or voltaic 
cell 31 

Fundamental Chemical Principles . 
Action of moist air upon bright iron or steel; Action of heat upon red 

oxide of mercury; Synthetic and analytical chemical processes . . 32 
Law of the conservation of matter; Chemical elements; Molecules; 

Atoms 33 

Atomic weights; Symbols and their formation 34 

Table of the atomic weights of the most important chemical elements, 
together with their symbols and atomic weights; Valence of the 

elements . 36 

Equivalent weights or combining weights $7 

Arrangement of the most important elements according to their va- 
lence; Metals and non-metals and their classification. . . .38 



X CONTENTS. 

PAGB 

Metalloids; Properties of metals and non-metals 3Q 

Acids, bases, salts; Great affinity of the elements for oxygen . . 40 
Acids and their properties; Haloid acids; Oxy-acids; Bases; Hydroxyl 

group; Salts and their properties 41 

Neutralization; Reagent papers 42 

Formation of new products by the neutralization between acids and 

bases 43 

Formation of salts from the acids; Neutral salts 44 

Acid salts; Equations showing the difference between neutral and acid 

salts; Nomenclature of salts 45 

Fundamental Principles of Electro- Chemistry \ 
Electrolytes; Conductors and non-conductors; Conductors of the first, 



and of the second, class 

Electrolysis; Electrodes; Ions; Cations; Anions; Properties of the ions 
Theory of solutions; A solution not merely a mechanical mixture; Vari- 
ous kinds of solutions 

Experiment with cupric sulphate solution; Law followed by the gases 

Osmotic pressure 

Electrolytic dissociation; Clausius' theory; Raoult's method of de 

termining the molecular weights of dissolved bodies . 
Discovery, by Arrhenius, regarding the conductivity of solutions 
Migration of the ions; Energy; Definition of energy; Mechanical 

work ............ 

Force and counter-force; Law of the conservation of force and work 
Processes on the electrodes; Electrolysis of a solution of potassium 

disulphate ........... 

Electrolysis of very dilute hydrochloric acid, and of sodium hydroxide 

Electrolysis of a solution of cupric sulphate 

Electrolysis of a silver bath containing potassium-silver cyanide . 

Laws of Faraday 

Proportion of the quantity of substances which is separated on the 

electrodes, to the strength of the electric current 
Second law of Faraday as expressed by v. Helmholz; Electro-chemi 

cal equivalent, and its definition 

Table of electro-chemical equivalents; Solution-tension of metals. 
Osmotic theory of the production of the current, according to Nernst 

Process which takes places in a cell 

Determination of the electro-motive force of a cell 

Additional chemical processes which take place in a cell; Polarization 

and its occurrence. ......... 

Counter-current or polarization-current ...... 

Origin of the electro-motive force of the polarization-current; Decom 

position-pressure .......... 

Decomposition-values of solutions; Velocity of ions 
Transport-values of the ions 



46 
47 



49 

50 
5i 

52 
S3 

54 
55 
56 
57 
58 

59 

60 

61 

63 
64 

65 
66 

67 
68 
69 



CONTENTS. XI 



III. 

SOURCES OF CURRENT. 



CHAPTER III. 



Voltaic Cells, Thermo-Piles, Dynamo-Electric Machines, 
Accumulators. 

Voltaic cells; Conversion of chemical energy into electrical energy; 

Inconstant cells 70 

Constant cells; Voltaic pile; Trough battery; Local action; Amalga- 
mation 71 

Smee cell 72 

Avoidance of polarization; Daniell cell ....... 73 

Meidinger cell 74 

Bunsen cell; Artificial carbon 75 

Processes in the Bunsen cell; Forms of Bunsen cells . . . -76 
Improved Bunsen cell; Location of Bunsen cells . . . . .78 

Dupre's substitute for sulphuric and nitric acids for filling cells . . 79 
Treatment of Bunsen cells ......... 80 

Advisability of having duplicate set of porous clay cups; Renewal of 

the acid; Leclanche cell 81 

Cupric oxide cell 82 

Cupron cell 83 

Plunge batteries , 84 

Plunge battery constructed by Fein 85 

Stoehrer's plunge battery; Dr. G. Langbein's plunge battery . . 86 

Bichromate cell; Coupling cells 87 

Coupling for electro-motive force; Coupling for quantity of current, or 

parallel coupling; Mixed coupling or group coupling. . . .89 
Thermo-electric piles; Discovery by Prof. Seebeck . . . .90 

Noe's and Clamond's thermo-electric piles 91 

Giilcher's thermo-electric pile . . . . . . . .92 

Dynamo-electric machines ......... 93 

Fundamental principle of dynamo-electric machines . . . .94 

Windings; Armature 95 

Separate parts of the dynamo-machine; The frame; Magnetic winding 

or field winding; Two-polar and four-polar type of dynamo . . 96 
Remanent magnetism; Self excitation; Foreign or separate excitation; 
Armature or inductor; Ring armature; Drum armature; Ring arma- 
ture winding 97 

Drum armature winding 98 

Chief difference between the modes of winding 99 

Slotted armature; Commutator . . 100 



Xll CONTENTS. 

*AGE 

Brushes; Choice of material for the brushes; Copper and brass gauze 

brushes 101 

Boudreaux brushes; Brush holders; Brush rocker .... 102 

Direct current dynamos; Series wound machines; Shunt-wound 

dynamo 103 

Two-pole wound dynamos 104 

Compound -wound dynamos 105 

Multi-polar type of dynamo manufactured by The Hanson & Van 

Winkle Co., and its armature 106 

Motor-generator sets manufactured by the same firm .... 109 

Data for the most suitable machine . . . . . . . no 

Secondary cells (accumulators); Plante's practical application of ac- 
cumulators, and his accumulator in 

Use of lead grids by Faure; Chemical processes in the accumulator; 

Elb's theory 112 

Liebenow's theory; Common form of an accumulator; Maintenance of 

accumulators. . . . , 116 

Mode of charging a cell . . . . . . .. . -H7 

Coupling accumulators; Ampere hours capacity 118 



IV. 
PRACTICAL PART. 



CHAPTER IV. 

Arrangement of Electro-Plating Establishments in General. 

Light and ventilation in plating rooms 119 

Heating the plating room 120 

Renewal of water; Floors of plating rooms . . . . . . 121 

Size of plating rooms; Grinding and polishing rooms .... 122 

Exhaust fans 123 

Distance between machines; Transmission 124 

Electro-Plating Arrangements in Particular. 
Parts of the actual electro-plating plant; Current density . . . 124 
Electro-chemical equivalent of the ampere-hour; Determination of the 

quantity of deposit and the time required 126 

Determination of the current-output 127 

Electro-motive force in the bath; Determination of the resistance of 

the electrolyte 128 

Electro-motive counter force of polarization 130 

Determination of the electro-motive counter-force 131 

Scattering of the current lines. 132 



CONTENTS. Xlll 

PAGE 

A. INSTALLATION WITH CELLS. 

Coupling of cells 132 

Examples of coupling 133 

Current regulation 135 

Current regulator, resistance board, or rheostat; Conditions upon 

which the action of the resistance board is based .... 136 

Modes of coupling the resistance board 137 

Current indicator; Galvanometer 138 

The Hanson & Van Winkle patent underwriters' rheostat . . . 140 
The Hanson & Van Winkle Co.'s special rheostat .... 141 
Indications made by the galvanometer; Validity of the deductions 

drawn from the position of the needle 143 

Means of recognizing the polarity of the current; Measuring instru- 
ments; Ampere-meter or ammeter; Voltmeter 144 

Instruments constructed according to Hummel's patent . . . 145 

The Waverly voltmeter 146 

The Weston ammeter; Arrangement of the switch-board, and ammeter 

with a bath operated by means of a battery; Voltmeter switch . . 147 
Scheme showing the coupling of the main object-wire and of the main 

anode-wire, together with the resistance-boards, the voltmeter switch 

and two baths , 148 

Dependence of the current-density on the electro-motive force . . 151 
Conductors; Most suitable material for conducting the current; Loss of 

electro-motive force caused by conductors 152 

Mounting of conductors; Main and branch conductors; Dimensions of 

conductors 153 

Connection of main and branch conductors; Tanks; Welded steel tanks. 154 

Construction of wooden tanks; Lead-lined tanks 155 

Cement-lined tanks; Stoneware tanks . . . . ... . 156 

Insulating joint; Conducting fixtures; Conducting rods. . . . 157 

Binding posts and screws; Arrangement of objects and anodes in the 

bath 158 

Supply of anodes; Anode-hooks 159 

Slinging wires; Protection of the rods 160 

Apparatus for cleansing and rinsing; Cleansing the objects from grease; 

Special table for this purpose 161 

Drying the objects 163 

Centrifugal dryer 164 

B. INSTALLATION WITH DYNAMO-ELECTRIC MACHINES. 

Setting up and running a dynamo; Cause of most of the troubles with 
plating dynamos 164 

Foundations for dynamos; Mode of ascertaining the direction of rota- 
tion; Belting. 165 

Starting up; Proper position of the tips of the brushes; Adjustment of 
the brushes; Lubrication; Treatment of the commutator . . . 166 



XIV 



CONTENTS. 



PAGE 

Choice of a dynamo 167 

Impressed electro-motive force of the dynamo; Explanation by an ex- 
ample of the choice of a suitable dynamo 168 

Destruction of an excess of electro motive force ..... 169 
Advisability of using several dynamos with different impressed electro- 
motive forces 170 

Principle of series-coupling of baths illustrated; Connection of the 
baths, resistance boards and measuring instruments to a shunt- 
wound dynamo 171 

Parallel coupling and series-coupling of dynamo-machines; Rules to 

be observed in coupling several dynamos in parallel .... 172 
When the coupling of dynamos in series may become necessary . . 174 
Ground plan of an electro-plating plant with dynamo .... 175 
Plating room and method of connecting dynamo, tanks and instru- 
ments according to the two-wire system 179 

Three-wire system of current distribution; Plating room wired accord- 
ing to this system; Switch boards 180 

C. INSTALLATION AND ACCUMULATORS. 

Use of an accumulator; Dynamos for supplying the accumulator. . 184 
On what the magnitude of the performance of an accumulator de- 
pends; Ampere-hour capacity of an accumulator; Explanatory ex- 
ample 185 

Diagram of connections for using storage batteries in connection with 
dynamos 186 

CHAPTER V. 
Preparation of the Metallic Objects. 



a. mechanical treatment previous to electro-plating. 

Nature of the mechanical treatment; Formation of the deposit in cor 

respondence with the surface of the basis-metal . 
Scratch-brushing; Various forms of brushes .... 

Treatment of scratch-brushes 

Circular scratch-brushes and their construction 

Various kinds of brushes suitable for the different operations 

The sand-blast and its use in cleaning; Types of sand-blast . 

Cleaning metallic articles in the tumbling barrel or drum 

Adjustable oblique tumbling barrel; Grinding; Grinding wheels and 

their construction ....... 

Grinding wheels of paste-board and of cork waste . 
Elastic wheel; Reform wheel; Emery for gluing . 
Treatment of the grinding wheels; Vienna lime . 
Removing emery and glue from worn leather-covered wood polishing 

wheels, and machine for that purpose; Grinding lathes 



188 
189 
190 
191 
192 

193 
194 

196 
197 
198 
199 



CONTENTS. XV 

PAGE 

Belt attachment combined with a double grinding lathe; Types of elec- 
trically driven grinding motors 202 

Execution of grinding and brushing; Fiber brushes .... 204 

Grinding iron and steel articles 205 

Grinding brass and copper castings, sheets of brass, German silver, 

copper and zinc; Polishing 206 

Foot-lathe for polishing; Union canvas wheel; Universal polishing 

wheel 207 

Walrine wheel; Types of polishing lathes 208 

Independent spindle polishing and buffing lathe 210 

Electrically driven polishing and buffing lathes 211 

Belt-strapping attachment; Polishing materials 212 

Polishing with Vienna lime; Burnishing 213 

B. MECHANICAL TREATMENT DURING AND AFTER ELECTRO-PLATING. 

Scratch-brushing the deposits, and its object 213 

Porous formation of the deposit; Effect of scratch-brushing; Scratch- 
brushes for various purposes; Mode of operating with the hand 
■ scratch-brush ........... 214 

Scratch-brushing with the lathe brush; Drying the finished plated 

objects 215 

Freeing nickel objects from moisture; Production of high luster; 
Polishing deposits of nickel, copper and brass, gold, silver and 

platinum; Operation of burnishing 216 

Forms of burnishers; Cleansing the polished objects .... 217 

Chemical Treatment. 

Pickling and dipping; Pickle for cast-iron and wrought-iron articles; 
Cleansing badly rusted iron articles ....... 218 

Operation of pickling cast-iron ........ 219 

Pickling in the electrolytic way 220 

Bath for electrolytic pickling; Removal in the electrolytic way of the 
layer of hard solder remaining after soldering bicycle frames . . 221 

Duration of pickling 222 

Pickling zinc objects; Cleansing and brightening copper and its alloys; 

Preliminary pickle; Bright dipping bath 223 

Use of potassium cyanide as a pickle; Mat-dipping .... 224 

Preparation of a good mat dip; Mixture for the production of a mat- 
grained surface by pickling; Main points to be observed in pickling. 225 

Absorbing plant for escaping acid vapors 227 

Removal of grease and cleansing; Materials used for the purpose. . 228 
Preparation of lime mixture or paste; Electro-chemical cleaning. . 229 
Electro-chemical cleaning baths and their application .... 230 
Cleansing objects of iron and steel, copper, bronze, German silver and 
tombac 232 



XVI CONTENTS. 

PAGE 

Electro-Plating Solutions (Electrolytes, Baths). 

Solvents; Spring and well waters 233 

Distilled water, Rain water; Purity of chemicals; Examples of differ- 
ence in chemicals 234 

Concentration of the baths; Conclusions which may be drawn from the 

specific gravity 235 

Cause of dark or spotted nickeling; Difference in concentration in 

summer and in winter; Agitation of the baths 236 

Uneven wearing of the anodes 22,7 

Advantages claimed for constant agitation; Cause of changes in con- 
centration of the baths 238 

Temperature of the baths; Boiling the baths, and utensils for the pur- 
pose 240 

Use of nickeled kettles; Dissolving nickel salts soluble with difficulty; 

Working the bath with the current; Objections to this process. . 241 
Filtering the baths; Prevention of impurities; Choice of anodes . . 242 

Absorption of the deposit 243 

Effect of the current-density 244 

Current-output; Reaction of the baths 245 

General qualifications an electro-plating bath should possess . . 246 

CHAPTER VI. 

Deposition of Nickel and Cobalt. 

1. deposition of nickel. 

Growth and popularity of nickel plating; Properties of nickel . . 247 

Nickel salts 248 

Conducting salts 249 

Other additions to nickel baths; Boric acid 250 

Substitution of glycerin for water in the preparation of nickel baths . 251 
Effect of current-density; Electro-motive force; Reaction of nickel 

baths , 252 

Formulas for nickel baths 253 

Baths with the addition of chlorides 255 

Nickel baths containing boric acid 256 

Nickel baths for special purposes; For copper and copper alloys . . 258 
For zinc; Bath yielding a very fine dark nickeling .... 259 

Black nickeling 260 

Bath for iron and copper alloys; Baths for the production of very thick 

deposits 262 

Addition of carbon disulphide to nickel baths 263 

Nickel bath without nickel salt; Prepared nickel salts .... 264 
Correction of the reaction of nickel baths; Thick deposits in hot 

nickel baths 265 

Foerster's experiments; Dr. George Langbein's experiments; Quick 

nickeling; Dr. Kugel's discovery 266 



CONTENTS. XVII 

PAGE 

Thick deposits in cold nickel baths ....... 267 

Coehn and Siemens' experiments with electrolytes containing nickel 
salts and magnesium salts; Nickel anodes; Elliptic anodes patented 

by The Hanson & Van Winkle Co 268 

Objection to the use of insoluble anodes 271 

Proportion of cast to rolled anodes 273 

Cause of a reddish tinge on the anodes 274 

Uneven solution of the anodes; Scattering of current lines; Execu- 
tion of nickeling; Removal of grease from the objects . . . 275 
Previous coppering or brassing of certain objects; Security against rust. 276 
Nickeling parts of bicycles; Means for preventing the rusting of the 

basis-metal . 277 

Over-nickeling or burning and means of avoiding it . . . 278 

Normal deposition and criterion for judging it; Most suitable current- 
density for nickeling .......... 279 

Advisability of the use of a voltmeter and ammeter, as well as of a 

rheostat; Production of a very thick deposit; Solid nickeling . . 280 
Faulty arrangement of anodes; Suspension of the objects ... . 281 

Nickeling of cavities and profiled objects; Use of the hand anode; Ex- 
periments in nickeling the inside of brass tubes 282 

Polarization; Reason why iron requires a stronger current for nickel- 
ing than copper alloys, and zinc a stronger one than iron. . . 284 

Stripping defective nickeling 285 

Stripping acid 286 

Removal of the nickel coating by mechanical means; Stripping by 

electrolysis 287 

Remedy against the yellowish tone of the nickeling; Defective nickel- 
ing; Resume of the principal defects which may occur in nickeling, 

and remedies. 288 

Refreshing nickel baths 290 

Treatment of the articles after nickeling; Polishing nickel deposits; 

Cleansing polished objects 291 

Calculation of the nickeling operation . . . • . . . . 292 
Nickeling small and cheap objects in large quantities .... 293 

Types of mechanical electro-plating apparatus 295 

Lifting device for raising and lowering the plating barrel . . . 297 
Nickeling sheet-zinc; Preliminary grinding or polishing the sheets . 298 
Construction of cloth bobs; Mode of polishing the sheets . . . 299 
Automatic polishing machines ........ 300 

Freeing zinc sheets from grease . 301 

Nickeling the sheets; Advantages of coppering or brassing the sheets. 302 
Dimensions of tanks for nickeling the sheets; Anodes for nickeling 
sheet-zinc ............ 304 

Alkalinity of the baths for nickeling sheet-zinc; Polishing the nickeled 

sheets 305 

Nickeling tin-plate, copper and brass sheets, sheet-iron and sheet-steel. 306 



XV111 CONTENTS. 



Nickeling wire . . • 3°7 

Nickeling knife-blades, sharp instruments, etc 310 

Nickeling skates; Nickeling soft alloys of lead and tin . . . .311 
Nickeling printing plates; Hard nickeling and baths for that purpose. 312 
Recovery of nickel from old baths; Deposition of nickel alloys . . 314 

Nickel bronze; Deposit of German silver 315 

Examination of nickel baths; Determination of the content of acid . 316 
Methods for the examination of baths; Gravimetric analysis; Volu- 
metric analysis 3 l & 

Electrolytic method of analysis, and apparatus for that purpose . . 319 

2. DEPOSITION OF COBALT. 

Properties of cobalt; Baths for plating with cobalt; Cobalting copper 
plates for printing 323 

Determination of the quantity of copper dissolved in stripping the co- - 
bait deposit from cobalted copper plates; Warren's cobalt solution . 324 

CHAPTER VII. 
Deposition of Copper, Brass and Bronze. 
I. deposition of copper. 
Properties of copper; Copper baths; On what the composition of these 

baths depends 326 

Copper cyanide baths, and their preparation; Formation of cupric 

cyanide 3 2 7 

Stockmeyer's experiments; Hossauer's copper bath .... 328 

Copper baths for iron and steel articles 329 

Stockmeyer's copper bath 330 

Copper baths with sulphate of copper (blue vitriol) . . . .331 
Use of cupro-cupric sulphite for the preparation of copper baths; Cop- 
per bath recommended by Pfanhauser 332 

Copper bath for small zinc objects; Prepared copper salts . . . 333 
Copper baths without potassium cyanide; Bath for coppering zinc ob- 
jects; Weill's copper bath 334 

Walenn's and Gauduin's copper baths; Tanks for potassium-copper 

cyanide baths 335 

Copper anodes; Formation of slime on the anodes; Execution of 

copper-plating . . . 336 

Causes of copper baths yielding no deposit at all or only a slight one, 

and their remedies 337 

Scouring and pickling the articles to be coppered; Treatment of de- 
fective places of the deposit; Washing the coppered objects . . 338 
Prevention of stains; O. Schultz's method for removing hydrochloric 
acid from the pores and preventing the formation of stains; Polish- 
ing the coppered objects 339 

Penetration of the deposit into the basis-metal; Coppering sheet-iron 
or sheet-zinc; Treatment of copper baths when they become inactive. 340 



CONTENTS. XIX 

PAGE 

Coppering small articles in quantities; Inlaying of depressions of cop- 
pered art castings with black 341 

Examination of copper baths containing potassium cyanide . . . 342 

Determination of potassium cyanide . . 343 

Determination of copper by electrolysis 345 

Volumetric determination of copper 346 

2. DEPOSITION OF BRASS. 

Constitution and varieties of brass . 348 

Behavior of brass towards acids; Brass baths, their composition and 

preparation 349 

Rules for baths containing more than one metal in solution; Brass 

bath according to Roseleur t . . 350 

Other brass baths . . . . . . . . . . 351 

Use of cupro-cupric sulphite and cuprous oxide for the preparation of 

brass baths 352 

Bath for brassing zinc; Bath for brassing wrought iron, cast iron and 

steel . 353 

Solution for transferring any copper-zinc alloy which serves as anode; 

Irregular working of fresh baths; Prepared brass salts . . . 354 
Tanks for brass baths; Brass anodes; Execution of brassing; On what 

the color of the deposit depends 355 

Formation of slime on the anodes, and what it indicates . . . 356 
Remedies for the sluggish formation of the deposit .... 357 
Effect of too great an excess of potassium cyanide; Treatment of a 

brass bath that has not been used for some time .... 358 

Production of a brass deposit which is to show a tone resembling gold; 

Importance of the distance of the objects to be brassed from the 

anodes 359 

Brassing of unground iron casting; Examination of brass baths; De- 
termination of free potassium cyanide and the content of copper . 360 
Volumetric determination of zinc; Deposits of tombac .... 362 

• Deposits of bronze 363 

Method of preparing a bronze bath. 364 

CHAPTER VII. 

Deposition of Silver. 

Properties of silver 365 

Silver baths, their composition, preparation and treatment . . . 366 
Advantage of silver baths prepared with silver chloride. . . . 367 
Silver bath for a heavy deposit (silvering by weight); Preparation of a 

bath with silver chloride; Preparation of silver chloride . . . 368 
Preparation of a bath with silver cyanide; Preparation of silver cyanide. 369 
Silver bath for ordinary electro-silvering; Tanks for silver baths; Treat- 
ment of the silver baths; Silver anodes; Potassium cyanide required 
for the bath 370 



XX CONTENTS. 

PAGE 

Indication of the presence of too much or not enough potassium cyanide. 371 
The behavior and appearance of the anodes as criteria of the content of 
potassium cyanide in the bath; Regulating the content of potassium 

cyanide 37.2 

Keeping the bath constant by silver anodes ...... 373 

Proper treatment of baths made with silver chloride; Gradual thicken- 
ing of the baths 374 

Determination of the proper proportion of silver and excess of potas- 
sium cyanide in the bath; Agitation of silver baths; Contrivances to 

keep the articles in gentle motion 375 

Addition of certain substances to silver baths; Preparations for bright 

plating 377 

Yellow tone of silvering 379 

Silver alloys; Areas silver-plating 380 

Experiments in areas silver-plating 381 

Execution of silver-plating; Silver-plating by weight; Freeing from 

grease; Pickling and rubbing; Amalgamating (quicking). . . 382 
Slinging wires; Methods of depositing an extra heavy coating of silver 
on the convex surfaces of spoons and forks ..... 383 

Silver-plating the steel blades of table knives 385 

Determination of weight of deposit . 386 

Roseleur's plating balance 388 

Plating balance, together with rheostat, voltmeter ahd silver bath . 390 
Voltametric balance; Copper voltameter ...... 392 

Advantages and disadvantages of the voltametric balance . . . 393 

Neubeck's combination 394 

Voltametric controlling apparatus 396 

Calculation of the weight of the silver deposit from the current- 
strength used 398 

Mat silver 400 

Polishing the deposits; Ordinary silver-plating; Quicking solution; 
Direct silvering of Britannia, tin, German silver .... 401 

Australian patent for directly silver-plating iron and steel; Stopping- 
off, and varnish for that purpose ........ 402 

Special application of electro-silvering; Silvering of fine copper wire; 

Incrustations with silver and gold 403 

Imitation of niel or nielled silvering; Nielling upon brass . . . 404 

Old (antique) silvering; Oxidized silver 405 

Brown tone on silver 406 

Yellow color on silvered articles: Stripping silvered articles. . . 407 
Determination of silver-plating; Process for the determination of 

genuine silvering used by the German custom-house officers . . 408 
Examination of silver baths; Determination of free potassium cyanide, 
and of potassium carbonate ......... 409 

Calculation of the quantity of barium cyanide required for the con- 
version of the quantity of potassium carbonate found. . . . 410 



contp:nts. xxi 

PAGE 

Table for the use of a 20% per cent, barium cyanide solution; Deter- 
mination of the silver by the electrolytic method . . . .411 
Recovery of silver from old silver baths, etc. ..... 412 

CHAPTER IX. 
Deposition of Gold. 
Occurrence of gold; Properties of gold; Mode of expressing the fine- 
ness of gold; Testing gold by means of the touch-stone . . , 415 
Shell-gold or painters' gold; Gold baths their composition, prepara- 
tion and treatment . . . . . . . . . 416 

Baths for cold gilding; Effect of too large an excess of potassium cyanide. 417 
Bath with yellow prussiate of potash for cold gilding .... 418 

Baths for hot gilding 419 

Preparation of gold baths with the assistance of the electric current . 420 
Gold anodes; Management of gold baths; Use of insoluble platinum 

anodes; Use of steel anodes and experiments with them . . . 421 
Advantages claimed for steel anodes; Use of carbon anodes; Platinum 

anodes for coloring the deposit 423 

Cause of unsightly and spotted deposits; Tanks for gold baths . . 424 

Heating the baths 425 

Execution of gold-plating; Gilding without a battery; Preparation of 

the articles for gilding 426 

Current-strength for gilding; Agitation of the objects in the bath . 427 
Gilding the inner surfaces of hollow-ware; Process of gold-plating in 

the cold, and in the hot, bath 428 

Polishing the gold deposits , 429 

Red gilding; Determination of the content of copper required for 

obtaining a beautiful red gold 430 

Plating rings, watch chains, and other objects of base metal with red 

gold; Green gilding 431 

Rose-color gilding; Rose gold solution . 432 

Method of gilding which is a combination of fire-gilding with electro- 
deposition . 433 

Mat gilding; Matting with the sand blast and by chemical or electro- 
chemical means 434 

Coloring of the gilding 435 

Gilder's wax; Process to give gilded articles a beautiful, rich appear- 
ance 436 

Method of improving bad tones of gilding; Incrustations with gold; 
Gilding of metallic wire and gauze; J. W. Spaeth's machine for this 

purpose 437 

Stripping gold from gilded articles; Electrolytic smoothing and polish- 
ing scratched or rubbed rings 440 

Determination of genuine gilding; Examination of gold baths; De- 
termination of gold by the electrolytic method 441 

Recovery of gold from gold baths, etc 442 



XX11 CONTENTS. 

PAGE 

CHAPTER X. 
Deposition of Platinum and Palladium. 
I. deposition of platinum. 
Properties of platinum; Platinum baths, their composition, prepara- 
tion and treatment 444 

Boettger's bath; Preparation of platoso-ammonium chloride; Platinum 
bath patented by the Bright Platinum Plating Co.; Jordis's platinum 

bath 445 

Management of platinum baths; Execution of platinum plating . . 446 
Production of heavy deposits; Process for plating directly, without 
previous coppering, iron, nickel, cobalt, and their alloys with 

platinum 447 

Recovery of platinum from platinum solutions . . . . 448 

2. deposition of palladium. 

Properties of palladium 448 

Bertrand's palladium bath; Pilet's bath for plating watch movements. 449 

CHAPTER XI. 
deposition of tin, zinc, lead, and iron, 
i. deposition of tin. 
Properties of tin; Moire metallique on tin; Tin baths, their composi- 
tion, preparation and treatment 450 

Tinning of objects of zinc, copper, and brass; Experiments with Sal- 

zede's bronze bath 451 

Neubeck's bath; Management of tin baths; Process of tin-plating . 452 

2. DEPOSITION OF ZINC. 

Properties of zinc 453 

Value of electro-zincking. . . . . . . . 454 

Comparative experiments regarding zincking by the hot process and 
by electro-deposition; Disadvantages of hot galvanizing; Loss of zinc 
in electro-zincking .......... 455 

Drawbacks of both processes; Preece's test for judging the thickness 
of the coating of zinc obtained by hot galvanizing; Burgess's method 
of testing the power of resistance of coatings obtained by electro- 
zincking . . . . 456 

Zinc baths; Dr. Alexander's patented zinc bath 458 

Decision of the Circuit Court of the United States for the District of 
New Jersey in regard to the Alexander patent; Recent investigations 
regarding the electrolysis of zinc; Regenerative process . . . 459 
Addition of aluminium-magnesium alloy and of dextrose to zinc baths. 460 
Addition of pyridine, and of glucosides; Formula for an alkaline zinc 

bath 461 

Formulas for zinc baths; Importance of using zinc salts free from other 
metals 462 



CONTENTS. XX111 

PAGE 

Zinc anodes; Treatment of zinc baths 463 

Loss of zinc by the formation of basic zinc salts; Heating the baths for 

strongly profiled objects 464 

Tanks for zinc baths; Execution of zincking . . . . . 465 

Zincking of sheet iron 466 

Zincking of pipes , 467 

Zincking of wrought iron girders, T-i r o n > U-i ron > L.-i r °n, etc.; Pro- 
filed anodes 468 

Zincking of wire, steel tapes, cords, etc 469 

Zincking of screws, nuts, rivets, nails, tacks, etc.; Zinc alloys, and 
their deposition 47 1 

3. DEPOSITION OF LEAD. 

Properties of lead; Lead baths, their composition and preparation; 

Anodes for lead baths 47 2 

Metallo-chromes (Nobili's rings, iridescent colors, electrochromy) . 473 

4. DEPOSITION OF IRON (STEELING) . 

Principal practical use of the electro-deposition of iron; Iron (steel) 

baths, their composition and preparation 475 

Management of iron baths ......... 476 

Execution of steeling . . 477 

CHAPTER XII. 
Deposition of Antimony, Arsenic, Aluminium, 
i. deposition of antimony. 
Properties of antimony; Antimony baths, their composition and pre- 
paration; Explosive power of antimony deposits 478 

Non-explosive deposit of antimony; Antimony bath which yields good 
results . 479 

2. DEPOSITION OF ARSENIC. 

Properties of arsenic; Arsenic baths, their composition, preparation 

and treatment . . . . 479 

Cause of defective deposits 480 

Solutions for coloring articles black 481 

3. DEPOSITION OF ALUMINIUM. 

Non-feasibility of depositions of aluminium from aqueous solutions of 
its salts; Aluminium baths offered by dealers, and the results of test- 
ing them 483 

4. DEPOSITION UPON ALUMINIUM. 

Difficulties met with in the electro-deposition of other metals upon 
aluminium; Behavior of aluminium towards the usual cleansing 
agents 484 



XXIV CONTENTS. 

PAGE 

Coppering aluminium previous to plating and copper bath for this pur- 
pose; Villon's process of plating aluminium; Prof. Nees's process; 
Burgess and Hambuechen's method ....... 485 

Gottig's process; Electro-deposits upon aluminium produced by the 
Mannesmann Pipe Works, Germany 486 

CHAPTER XIII. 

Deposition by Contact, by Boiling, and by Friction. 
Theory of contact-deposition; Deposits by immersion or boiling; Plat- 
ing by means of a brush or by friction. . . ". . . . 487 
Limits of the application of the contact-process; Drawbacks of the 

process 488 

Contact-metals; Properties of the electrolytes for the contact-process . 489 
Means of increasing the conductivity of the electrolytes containing 
potassium cyanide; Promotion of the attack of the contact-metal; 
Plating small objects in quantities; Useless reduction of metal in 

contact-deposition 4go 

Methods to avoid the reduction of metal on the wrong place; Defects 
of the contact-process; Nickeling by contact and boiling; Stolba's 

process of nickeling . 491 

Processes for nickeling small articles; Use of aluminium-contact in 

place of zinc-contact 492 

Darlay's patented process of nickeling 493 

Chemical process of Darlay's electrolyte; Cobalting by contact and 

boiling 494 

Coppering by contact and dipping; Liidersdorff's solution; Bacco's 

copper bath .' 495 

Darlay's patented bath 496 

Chemical process of Darlay's formula; Brush coppering . . . 497 
Coppering iron and steel objects, steel pens, needles' eyes, etc.; Brass- 
ing by contact; Darlay's bath 498 

Silvering by contact, immersion and friction; Bath for contact-silver- 
ing of copper and brass objects 499 

Darlay's patented bath; Silvering by immersion and solution for this 

purpo'se 500 

Preparation of solution of sodium sulphite 501 

Ebermayer's silver immersion-bath; Process of coating with a thin 

film of silver small articles, such as hooks and eyes, pins, etc. . . 503 
Cold silvering with paste; Composition of the argentiferous paste . 504 

Graining; Process of graining parts of watches 505 

Preparations for graining; Preparation of silver powder . . . 506 

Composition of resist 507 

Gilding by contact, by immersion, and by friction; Formulas for con- 
tact gold baths 508 

Gilding by immersion (without battery or contact) and formulas for 
this purpose 509 



CONTENTS. XXV 



Gilding by friction; Reddish gilding by friction; Solution for gilding 
by friction . . . . . . . ... • • • 5!0 

Platinizing by contact; Tinning by contact and by boiling; Baths for 
tinning by contact 5 11 

Zilken's patented bath for tinning by contact; Darlay's cold tin bath; 
Tinning solution for iron and steel articles 5 12 

Tinning solutions for small brass and copper articles . . . . 513 

A characteristic method of tinning by Stolba; Zincking by contact, 
and solution for this purpose; Darlay's bath; Process for coating 
brass and copper with a bright layer of zinc 514 

Deposition of antimony and of arsenic by immersion . . . . 515 

CHAPTER XIV. 
Coloring of Metals. 

Means by which metal coloring may be effected; Requirements for the 
practice of coloring 5*6 

Coloring of copper; Production of all shades from the pale red of cop- 
per to a dark chestnut-brown; Brown color on copper; Brown layer 
of cuprous oxide on copper; Brown of various shades on copper . 518 

Brown on copper by the Chinese process; Gold-yellow on copper; 
Manduit's process of bronzing copper; Yellowish-brown on copper . 519 

Dark brown to black on copper; Red to violet shades on copper; 
Cuivre-fumk 

Black color on copper; Mat-black on copper .... 

Patina; Definitions of patina and patinizing; Artificial patina- 
cesses of patinizing ........ 

Donath's process; Imitation of genuine green patina . 

Blue-green patina; Brown patina; Patina for copper and brass; 
gray on copper 

Various colors upon massive copper; Coloring brass and bronzes 

Lustrous black on brass; Black color on brass optical instruments . 526 

Steel-gray on brass; Silver color on brass; Pale gold color on brass; 
Straw color, to brown, through golden yellow, and tombac color on 
brass; Color resembling gold on brass 5 2 7 

Brown color called bronze Barbidienne on brass 5 2 8 

Coloring bronze articles dead-yellow or clay-yellow; Coloring brass 
articles in large quantities brown by boiling; Violet and cornflower 
blue on brass. . 5 2 9 

Ebermayer's experiments in coloring brass 530 

Coloring zinc; Black on zinc 53 1 

Gray, yellow, brown to black colors upon zinc; Brown patina on zinc; 
Various colors on zinc S3 2 

Gray coating on zinc; Bronzing, and yellow shades on zinc; Coloring 
iron; Browning gun barrels; Lustrous black on iron. . . . 533 

Meritens' process for obtaining a bright black color on iron. . . 534 



Pro- 



520 
5 2 i 

522 

523 



Steel 

• 5 2 4 

• 5 2 5 



XXVI CONTENTS. 

PAGE 

Mat black coating upon clock cases of iron and steel — Swiss mat; Blue 
color on iron and steel; Brown-black coating with bronze luster on 
iron; To give iron a silvery appearance with high luster . . . 535 

Coloring of tin; Bronze-like patina on tin; Sepia-brown tone upon 
tin; Dark coloration upon tin; Electrochroma ..... 536 

CHAPTER XV. 

Lacquering. 

Application of lacquer; Drying the lacquered objects .... 538 
Development in the art of lacquer making, and most noted improve- 
ments in lacquers; Pyroxyline lacquers, and their properties . . 539 

Lacquering by dipping 540 

Appearance of rainbow colors upon objects lacquered with pyroxyline 
lacquer; Production of various shades of color; Special invisible 
lacquer for ornamental cast and chased interior grille, rail and en- 
closure work 541 

Satin finish lacquer; Dip lacquer for pickled castings to be copper- 
plated and oxidized 542 

Helios dip lacquer; Old brass or brush-brass finishes .... 543 

Brush-brass finish lacquers . . . 544 

Egyptian brush-brass dip lacquer and brush-brass thinner; Brass bed- 
stead lacquering 545 

Dead black lacquers 546 

Dead black lacquer as a substitute for Bower-Barff .... 547 
Spraying of lacquers; The spraying machine and its application . . 548 

Equipment to be used ' . . . 549 

Management of lacquers for spraying 550 

Lacquers for spraying manufactured by The Egyptian Lacquer Manu- 
facturing Co.; Spraying black lacquers; Priming lacquer . . 551 

Water-dip lacquers and their use . 553 

Points to be followed when using water-dip lacquers .... 554 

CHAPTER XVI. 
Hygienic Rules for the Workshop. 

Neutralization of the action of acid upon the enamel of the teeth and 
the mucous membranes of the mouth and throat; Protection against 
the corrosive effect of lime and caustic lye; Vessels used in the 
establishment not to be used for drinking purposes .... 555 

Precautions in handling potassium cyanide and its solutions; Sensi- 
tiveness of many persons to nickel solutions; Poisoning by prussic 
acid, potassium cyanide and by cyanide combinations; Poisoning by 
copper salts 556 

Poisoning by lead salts; by alkalies; by mercury salts; by sulphuretted 
hydrogen; by chlorine, sulphurous acid, nitrous and hyponitric gases. 557 



CONTENTS. XXV11 

PAGE 

CHAPTER XVII. 
Galvanoplasty (Reproduction). 

Definition of galvanoplasty proper; Application of galvanoplasty; In- 
vention of the process .......... 558 

I. GALVANOPLASTY IN COPPER. 

Properties of copper deposited by electrolysis; Composition of the 

bath for depositing copper; Investigations by Hiibl and by Forster. 559 
Formation of spongy and sandy deposits; Investigations by Mylius 

and Fromm, and by Lenz and Soret 560 

Classification of the processes used in galvanoplasty; Galvanoplastic 
deposition in the cell apparatus; Simple apparatus frequently used . 561 

Large apparatus; French form of cell apparatus 562 

German form of cell apparatus 563 

Copper bath for the cell apparatus 564 

Freeing the bath from an excess of sulphuric acid; Decrease of the 
content of copper in the bath; Table of the content of blue vitriol at 

different degrees of Baume 565 

Electro-motive force in the cell-apparatus, and its regulation; Galvano- 
plastic deposition by the battery and dynamo; Arrangement for the 

employment of an external source of current 566 

Regulation of the current; Deposition with the battery; Cells . . 567 
Deposition with the dynamo; Dynamos suitable for the purpose; 

Electro-motive force for the slow process 568 

Combination of dynamos with a motor-generator ..... 569 

Coupling the baths; Coupling in series 570 

Mixed coupling or coupling in groups 571 

Electro-motive force with baths coupled in parallel, and with baths 

coupled in groups 57 2 

Combined operation with dynamo and accumulators; Disadvantage of 

interrupting the galvanoplastic deposition of copper .... 573 
Copper bath for galvanoplastic deposition with a separate source of 

current; Functions of the sulphuric acid 574 

Bath for the reproduction of shallow as well as of deep moulds; Prop- 
erties of the deposited copper; Bath for copper printing plates; 
Influence of the temperature of the electrolyte on the mechanical 

properties of the copper 575 

Current conditions; Color of the deposit as a criterion of the quality . 576 

Table showing the results of Hiibl's experiments 577 

Causes of brittle copper deposits; Forster's and Hiibl's investigations. 578 
E. Miiller and P. Behntje's investigations on the effects of organic 
additions; Duration of deposition. ....... 579 

Table of the duration of deposition for electrotypes 0.18 millimeter 
thick with different current-densities; Nitrate baths . . . . 580 

Agitation of the baths 581 



XXV111 CONTENTS. 

PAGE 

Sand's experiments . 582 

Stirring contrivances; Agitation of the bath by blowing in air; Agita- 
tion by flux and reflux . 583 

Arrangement of the baths for this purpose 584 

Necessity of keeping agitated baths clean; Filtering; Maximowitschs' 

, plan for agitating the baths 585 

Anodes; Effect of impurities in the anodes; Anode slime . . . 586 
Forster's experiments; Tanks; Rapid galvanoplasty .... 587 
Principles upon which the process of rapid galvanoplasty is based . 588 
Bath for shallow impressions" of autotypes, wood-cuts, etc.; Heating 
the bath; Danger of the crystallization of blue vitriol; Agitation of 

the bath. . . . • . 590 

Current-density for this bath; Knight's process of coppering matrices. 591 

Bath for deep depressions; Rudholzner's process 592 

Quality of the copper deposit; Treatment of rapid galvanoplastic 

baths 593 

Examination of the acid copper baths; Determination of free acid; 
Volumetric determination of the content of copper . . . . 594 

Electrolytic determination of the copper. 595 

Operations in galvanoplasty for graphic purposes; Preparation of the 

moulds (matrices) in plastic material . 596 

Moulding in gutta-percha, and in wax 597 

Mixtures for moulding in wax 598 

Wax-melting kettles; Preparing the wax for receiving the impression; 

Moulding box . . . 599 

Modern method of operation; Presses; The toggle press . . . 600 

Hydraulic press 601 

Metal matrices 602 

Dr. E. Albert on the rational preparation of metal matrices. . . 603 
Basis for the solution of the problem; Explanation of the process. . 605 

Fischer's process; Kunze's method , . . 609 

Further manipulation of the moulds; Removal of inequalities and eleva- 
tions; Making the moulds conductive; Black-leading the moulds and 

machines for this purpose 610 

Black-leading by the wet process 612 

Electrical contact; Trimming and wiring gutta-percha moulds; Feelers; 

Preparation of gutta-percha moulds for suspension in the bath . . 613 
Process for black-leaded wax moulds; Hook for suspension in the 
bath; Preventing the copper deposit from spreading; Treatment of 

very deep forms 614 

Suspending the moulds in the bath; Detaching the deposit or shell 
from the mould . . . . . . . . . . .615 



Moulding and melting table for wax moulds 
Backing the deposit or shell . 
Finishing; Saw table . . ... 
Planing or shaving machines . 



616 
617 
618 
619 



CONTENTS. XXIX 



Copper deposits from metallic surfaces; Process of making a copy 
directly from a metallic surface without the interposition of wax or 

gutta-percha 620 

Coppering stereotypes 622 

Coppering zinc plates; Preparation of type matrices; Treatment of 

originals of hard lead or similar alloys; Electro-etching . . . 623 
Covering or etching ground; Work of the engraver .... 624 
Photo-engraving and processes used ....... 625 

Photo-galvanography 626 

Collographic printing; Zincography 627 

Process of transferring hy reprinting 628 

Etching with the assistance of the electric current .... 629 

Heliography 630 

Electro-engraving; Rieder's patented process ..... 631 

Apparatus for electro-engraving ........ 632 

Galvanoplastic reproduction of plastic objects; Reproduction of busts, 
vases, etc.; Materials for the moulds . . . . -, s . . . 634 

Moulding surfaces in relief and not undercut; Dissection of the ob- 
jects; Moulding with oil gutta-percha . 635 

Preparation of oil gutta-percha; Moulding with gutta-percha; Metallic 

moulds, and metallic alloys for this purpose 636 

Plaster of Paris moulds and their preparation. ..... 637 

Moulding large objects 638 

Rendering plaster-of-Paris moulds impervious ..... 639 
Metallizing or rendering the moulds conductive; Metallization by the 

dry way; Metallization by metallic powders 640 

Metallization by the wet way 641 

Parkes' method of metallization 642 

Lenoir's process— Galvanoplastic method for originals in high relief . 643 
Gelatine moulds, and directions for making them. .... 644 
Special applications of galvanoplasty; Nature printing .... 645 

Production of copper tubes; Corvin's niello 646 

Plates for the productions of imitations of leather; Incrusting galvano- 
plasty ... 647 

Rendering the objects impervious 648 

Copper bath and current conditions; Neubeck's investigations of the 
work in the cell-apparatus; Additional manipulation of the deposits; 
Philip's process of coating laces and tissues with copper . . . 649 
Coating grasses, leaves, flowers, etc., with copper; Providing wooden 
handles of surgical instruments with a galvanoplastic deposit of cop- 
per; Coppering busts and other objects of terra-cotta, stoneware, 

clay, etc. . 650 

Protecting mercury vessels of thermometers by a galvanoplastic de- 
posit of copper; Coppering mirrors; Galvanoplastic decorations on 
glass and porcelain ware 651 



XXX CONTENTS. 



PAGE 



A. A. LeFort's process for silver deposit on glass and china; Prepara- 
tion of metallized silver 652 

Grinding the paint 653 

Firing the objects 654 

Plating the objects, and bath for this purpose 655 

Decorating umbrella and cane handles of celluloid with a metallic de- 
posit; Coppering baby shoes, carbon pins and carbon blocks, rolls of 
steel and cast iron, pump pistons, etc., steel gun barrels, candela- 
bra, stairs, and structural parts of buildings of rough castings . . 656 

II. GALVANOPLASTY IN IRON (STEEL) . 

First production of serviceable iron electrotypes; Klein's bath . . 657 
Lenz's investigations; Dr. George Langbein's investigations . . 658 
Precautionary measures to counteract the spoiling of the deposits; 

Contrivance for mechanically interrupting the current . . . 659 
Neubeck's experiments; Properties of electrolytically deposited iron; 

Advantages of^teeled copper electrotypes 660 

III. GALVANOPLASTY IN NICKEL. 

Production of nickel electrotypes in an indirect way .... 661 
Cold nickel bath for the direct method; Requirements for working with 

the direct process of deposition . . . . . . . . 662 

Most suitable electro-motive force; Devices for preventing the nickel 

deposit from rolling off 663 

Nickel matrices 664 

Mode of effecting an intimate union of the copper casing with the 

nickel ............. 665 

Matrices of massive nickel and cobalt . 666 

IV. GALVANOPLASTY IN SILVER AND GOLD. 

Difficulties in the preparation of reproduction in silver and gold; 
Moulding of the originals . . . . . . . . , 667 

Baths for galvanoplasty in silver, and in gold 668 

CHAPTER XVIII. 
Chemicals Used in Electro-Plating and Galvanoplasty. 

1. acids. 

Sulphuric acid (oil of vitriol) 669 

Recognition of sulphuric acid; Nitric acid (aqua fortis, spirit of nitre) 
and its recognition; Hydrochloric acid (muriatic acid) and its recog- 
nition; Hydrocyanic acid (prussic acid) 670 

Recognition of hydrocyanic acid; Citric acid and its recognition; Boric 
acid (boracic acid) and its recognition 671 

Arsenious acid (white arsenic, arsenic, ratsbane) and its recognition; 
Chromic acid and its recognition; Hydrofluoric acid . . . . 672 

Recognition of hydrofluoric acid . . . . . . . 673 



CONTENTS. XXXI 



II. ALKALIES AND ALKALINE EARTHS. 

Potassium hydrate (caustic potash); Sodium hydrate (caustic soda); 

Ammonium hydrate (ammonia or spirits of hartshorn) . . . 67s 
Recognition of ammonium hydrate; Calcium hydrate (burnt or quick 

lime) 674 

III. SULPHUR COMBINATIONS. 

Sulphuretted hydrogen (sulphydric acid, hydrosulphuric acid) and its 
recognition; Potassium sulphide (liver of sulphur) .... 674 

Recognition of potassium sulphide; Ammonium sulphide (sulphydrate 
or hydrosulphate of ammonium) ; Carbon disulphide or bisulphide; 
Antimony sulphide; Black sulphide of antimony [stibium sulfuratum 
nigrum); Red sulphide of antimony {stibium sulfuratum aurantia- 
cum); Arsenic trisulphide or arsenious sulphide (orpiment) . . 675 

Ferric sulphide. . . 676 

IV. CHLORINE COMBINATIONS. 

Sodium chloride (common salt, rock salt) and its recognition; Am- 
monium chloride (sal ammoniac) and its recognition; Antimony 
trichloride (butter of antimony) 676 

Arsenious chloride; Copper chloride; Tin chloride — a. Stannous chlo- 
ride or tin salt and its recognition, b. Stannous chloride; Zinc chlo- 
ride (hydrochlorate or muriate of zinc) ; Butter of zinc, and its recog- 
nition 677 

Chloride of zinc and ammonia; Nickel chloride and its recognition; 
Cobaltous chloride and its recognition; Silver chloride . . . 678 

Recognition of silver chloride; Gold chloride (terchloride of gold, 
auric chloride) and its recognition; Platinic chloride and its recog- 
nition 679 

V. CYANIDES. 

Potassium cyanide (white prussiate of potash) 680 

Comparative table of potassium cyanide with different content; Copper 

cyanide and its recognition 682 

Zinc cyanide (hydrocyanate of zinc, prussiate of zinc); Silver cyanide 
(prussiate or hydrocyanate of silver) ; Potassium ferrocyanide (yellow 
prussiate of potash), and their recognition ...... 683 

VI. CARBONATES. 

Potassium carbonate (potash) and its recognition; Acid potassium 
carbonate, commonly called bicarbonate of potash; Sodium car- 
bonate (washing soda); Sodium bicarbonate (baking powder) . . 684 

Calcium carbonate (marble, chalk); Copper carbonate, zinc carbonate, 
nickel carbonate, and their recognition 685 

Cobaltous carbonate 686 



XXX11 CONTENTS. 



VII. SULPHATES AND SULPHITES. 

Sodium sulphate (Glauber's salt); Ammonium sulphate, potassium- 
aluminium sulphate (potash-alum), and their recognition; Alu- 
minium-alum ........... 686 

Recognition of aluminium-alum; Ferrous sulphate (sulphate of iron, 
protosulphate of iron, copperas, green vitriol), and its recognition; 
Iron-ammonium sulphate; Copper sulphate (cupric sulphate, blue 
vitriol or blue copperas) , and its recognition 687 

Zinc sulphate (white vitriol), nickel sulphate, and their recognition; 
Nickel-ammonium sulphate ......... 688 

Recognition of nickel-ammonium sulphate; Cobalt-ammonium sul- 
phate; Sodium sulphite and its recognition; Sodium bisulphite . 689 

Cuprous sulphite . . . . 690 

VIII. NITRATES. 

Potassium nitrate (saltpetre, nitre), and its recognition; Sodium 
nitrate (cubic nitre or Chile saltpetre) ; Mercurous nitrate. . . 690 

Mercuric nitrate (nitrate of mercury), and its recognition; Silver 
nitrate (lunar caustic) . . . . 691 

IX. PHOSPHATES AND PYROPHOSPHATES. 

Sodium phosphate, sodium pyrophosphate, and their recognition; 
Ammonium phosphate 692 

X. SALTS OF ORGANIC ACIDS. 

Potassium bitartrate (cream of tartar) 692 

Potassium-sodium tartrate (Rochelle or Seignette salt), and its recog- 
nition; Antimony potassium tartrate (tartar emetic), copper acetate 

(verdigris) and their recognition 693 

Lead acetate, and its recognition; Sodium citrate 694 

Appendix. 

Contents of vessels; To find the number of gallons a tank or other 
vessel will hold; Avoirdupois weight; Troy weight .... 695 

Imperial fluid measure; Table of useful numerical data; To convert 
Fahrenheit thermometer degrees (F.) to Centigrade degrees (C); 
To convert Centigrade degrees to Fahrenheit degrees . . . 696 

Table for the conversion of certain standard weights and measures . 697 

Table of solubilities of chemical compounds commonly used in electro- 
technics. 798 

Content of metal in most commonly used metallic salts. . . 700 

Table showing the electrical resistance of pure copper wire of various 
diameter; Resistance and conductivity of pure copper at different 
temperatures 701 

Table of hydrometer degrees according to Baume, at 63.5° F., and 
their weights by volume; Table of bare copper wire for low voltages. 702 

Index . . . . • . 703 



ELECTRO-DEPOSITION OF METALS. 



i. 

HISTORICAL PART. 



CHAPTER I. 

HISTORICAL REVIEW OF ELECTRO-METALLURGY. 

In reviewing the history of the development of electrolysis, 
i. e., the reduction of a metal or a metallic alloy from the 
solution of its salts by the electric current, the simple reduc- 
tion which takes place by the immersion of one metal in the 
solution of another, may be omitted. This mode of reduction 
was well known to the alchemist Zozimus, who described the 
reduction of copper from its solutions by means of iron, while 
Paracelsus speaks of coating copper and iron with silver by 
simple immersion in a silver solution. 

Before the discovery, in 1789, of contact-electricity by Luigi 
•Galvani, there was nothing like a scientific reduction of 
metals by electricity ; and only in 1799 did Alexander Volta, 
of Pavia, succeed in finding the true causes of Galvani's dis- 
covery. Galvani observed, while dissecting a frog on a table, 
whereon stood an electric machine, that the limbs suddenly 
became convulsed by one of his pupils touching the crural 
nerve with the dissecting-knife at the instant of taking a spark 
from the conductor of the machine. The experiment was 
several times repeated, and it was found to answer in all cases 
when a metallic conductor was connected with the nerve, but 
not otherwise. He observed that muscular contractions were 
1 



Z ELECTRO-DEPOSITION OF METALS. 

produced by forming a connection between two different 
metals, one of which was applied to the nerve, and the other 
to the muscles of the leg. Similar phenomena having been 
found to arise when the leg of the frog was connected with 
the electric machine, it could scarcely be doubted that in both 
cases the muscular contractions were produced by the same 
agent. From a course of experiments, Galvani drew the 
erroneous inference that these muscular contractions wero 
caused by a fluid having its seat in the nerves, which 
through the metallic connections flowed over upon the mus- 
cles. Everywhere, in Germany, England and France, emi- 
nent scientists hastened to repeat Galvani's experiments, in 
the hope of discovering in the organism a fluid which they 
considered the vital principle ; but it was reserved to Volta to 
throw light upon the prevailing darkness. In his repeated 
experiments this eminent philosopher observed that one cir- 
cumstance had been entirely overlooked, namely, that in 
order to produce strong muscular contractions in the frog-leg 
experiment, it was absolutely necessary for the metallic con- 
nection to consist of two different metals coming in contact 
with each other. From this he drew the inference that the 
agent producing the muscular contractions was not a nerve- 
fluid, but was developed by the contact of dissimilar metals, 
and identical with the electricity of the electric machine. 

This discovery led to the construction of what is known as 
the pile of Volta, or the voltaic pile. The same philosopher 
found that the development of electricity could be produced by 
building up in regular order a pile of pairs of plates of dis- 
similar metals, each pair being separated on either side from 
the adjacent pairs by pieces of moistened card-board or felt 
On account of various defects of the voltaic pile, Cruikshank 
soon afterwards devised his well-known trough battery, which 
consisted of square plates of copper and zinc soldered together, 
and so arranged and fastened in parallel order in a wooden 
box that between each pair of plates a sort of trough was 
formed, which was filled with acidulated water. 



HISTORICAL REVIEW OP ELECTRO-METALLURGY. 3 

Nicholson and Carlisle, in 1800, were the first to decompose 
water electrolytically into hydrogen and oxygen, using a 
Volta pile. The method has only acquired practical im- 
portance during the last few years. Wollaston, in 1801, found 
that if a piece of silver in contact with a more positive metal, 
for instance, zinc, be immersed in copper solution, the silver 
will be coated with copper, and this coating will stand 
burnishing. 

Cruikshank, in 1803, investigated the behavior of solutions 
of nitrate of silver, sulphate of copper, acetate of lead, and of 
several other metallic salts, towards the galvanic current, and 
found that the metals were so completely reduced from their 
solutions by the current as to suggest to him the analysis of 
minerals by means of the electric current. 

To Brugnatelli we owe the first practical results in electro- 
gilding. In 1805, he gilded two silver medals by connecting 
them by means of copper wire with the negative pole of the 
pile, and allowing them to dip in a solution of fulminating 
gold in potassium cyanide, while a piece of metal was sus- 
pended in the solution from the positive pole. He also ob- 
served that the positive plate, if it consisted of an oxidizable 
metal, was dissolved. 

One of the greatest discoveries connected with the subject, 
however is that of Sir Humphry Davy, in 1807, when by 
decomposing potassium hydroxide and sodium hydroxide by ' 
means of a powerful electric current he obtained the metals 
potassium and sodium. 

Prof. Oersted, of Copenhagen, in 1820, found that the mag- 
netic needle is deflected from its direction by the electric 
current. It was known long before this that powerful electric 
discharges affect the magnetic needle. It had, for instance, 
been observed that the needle of a ship's compass struck by 
lightning had lost its property of indicating the North Pole, 
and several physicists, among them Franklin, had succeeded 
in producing the same phenomena by heavy discharges of the 
electrical machine, but they were satisfied with the supposition 



4 ELECTRO-DEPOSITION OF METALS. 

that the electric current acted mechanically, like the blow of 
a hammer. Oersted first perceived that electricity must be in 
a state of motion in order to act upon magnetism. This led 
to the construction of the galvanoscope or galvanometer, an 
instrument which indicates whether the cells or other source 
of current furnish a current or not, and by which the intensity 
of the source of current may also to a certain degree be 
recognized. 

Ohm, in 1827, discovered the law named after him, that the 
strength of a continuous current is directly proportional to the 
difference of potential or electro-motive force in the circuit, and 
inversely proportional to the resistance of the circuit. This law 
will be more fully discussed in the theoretical part. 

Ohm's discovery was succeeded, in 1831, by the important 
discovery of electric induction by Faraday. By induction is 
understood the production of an electric current in a closed 
circuit which is in the immediate proximity of a current- 
carrying wire. Faraday further found that the current in- 
duced in the contiguous wire is not constant, because after a 
few oscillations the magnetic needle returned to the position 
occupied by it before a current was passed through the current- 
carrying wire; whilst, when the current was broken, the needle 
deflected in the opposite direction. 

In the year following the discovery of Faraday, Pixii, of 
Paris, constructed the first electro-magnetic induction machine. 

Faraday's electrolytic law of the proportionality of the cur- 
rent-strength and its chemical action, and that the quantities 
of the various substances which are reduced from their combi- 
nations by the same current are proportional to their chemical 
equivalents, was laid down and proved in 1833, and upon 
this Faraday based the measurements of the current-strength 
by chemical deposition, as, for instance, that of water, in the 
voltmeter. 

Of the practical electro-chemical discoveries there remains 
to be mentioned the production of iridescent colors, in 1826, 
by Nobili, and the production of the amalgams of potassium 
and sodium, in 1853, by Bird. 



HISTORICAL REVIEW OP ELECTRO-METALLURGY. 5 

The actual galvanoplastic process, however, dates from 1838. 
In the spring of that year Prof. Jacobi made known to the 
Academy of Sciences of St. Petersburg his discovery of the 
utility of galvanic electricity as a means of reproducing objects 
of metal. He produced an exact mould of metals and artistic 
objects by means of wax or plaster, and then coated every 
detail of the surface of this mould with very fine graphite, 
thus rendering it electrically conductive. He then suspended 
the mould from the negative pole (cathode) of an electrolytic 
bath containing a suitable metallic salt, and formed the posi- 
tive pole of the same metal ; on passing an electric current 
through this bath the mould became lined with very fine 
particles of metal, forming a continuous and compact surface. 
The metal forming the anode was gradually dissolved in the 
bath as fast as it was deposited on the cathode. Hence, 
Jacobi must be considered the father of galvanoplasty in so 
far as he was the first to utilize and give practical form to the 
discoveries made up to that time. 

Though Jacobi's process was published in the English 
periodical, " The Athenaeum," of May 4, 1839, Mr. T. Spencer, 
who read a paper on the same subject, September 13, 1839, 
before the Liverpool Polytechnic Society, claimed priority of 
invention, as was also done by Mr. C. J. Jordan, who, on May 
22, 1839, sent a letter to the " London Mechanical Magazine," 
which was published on June 8, 1839. 

From this time forward the galvanoplastic art made rapid 
progress, and by the skill and enterprise of such men as the 
Elkingtons, of Birmingham, and De Ruolz, of Paris, it was 
speedily added to the industrial arts. 

Though copies of metallic objects by means of galvanoplasty 
could now be made, the employment of the process was re- 
stricted to metallic objects of a form suitable for the pdrpose, 
until, in 1840, Murray succeeded in making non-metallic sur- 
faces conductive by the application of graphite (black lead, 
plumbago), which rendered the production of galvanoplastic 
copies of wood-cuts, plaster-of-Paris casts, etc., possible. 



6 ELECTRO-DEPOSITION OF METALS. 

Dr. Montgomery, in 1843, sent to England samples of gutta- 
percha, which was soon found to be a suitable material for the 
production of negatives of the original models to be reproduced 
by galvanoplasty. 

Though it was now understood how to produce heavy de- 
posits of copper, those of gold and silver could only be obtained 
in very thin layers. Scheele's observations on the solubility 
of the cyanide combinations of gold and silver in potassium 
cyanide, led Wright, a co-worker of the Elkingtons, to employ, 
in 1840, such solutions for the deposition of gold and silver, 
and it was found that deposits produced from these solutions 
could be developed to any desired thickness. The use of 
solutions of metallic cyanides in potassium cyanide prevails at 
the present time, and the results obtained thereby have not 
been surpassed by any other practice. 

From the same year also dates the patent for the deposition 
of nickel from solution of nitrate of nickel, which, however, did 
not attract any special attention. This may have been chiefly 
due to the fact that the deposition of nickel from its nitrate 
solution is the most imperfect and the least suitable for the 
practice. 

To Mr. Alfred Smee we owe many discoveries in the deposi- 
tion of antimony, platinum, gold, silver, iron, lead, copper, and 
zinc. In publishing his experiments, in 1841, he originated 
the very appropriate term " electro-metallurgy " for the process 
of working in metals by means of electrolysis. 

Prof. Boettger, in 1842, pointed out that dense and lustrous 
depositions of nickel could be obtained from its double salt, 
sulphate of nickel with sulphate of ammonium, as well as from 
ammoniacal solution of sulphate of nickel ; and that such de- 
posits, on account of their slight oxidability, great hardness, 
and elegant appearance, were capable of many applications. 
However, Boettger's statements fell into oblivion, and only in 
later years, when the execution of nickeling was practically 
taken up in the United States, his labors in this department 
were remembered in Germany. To Bcettger w T e are also in- 



HISTORICAL REVIEW OP ELECTRO-METALLURGY. 7 

■debted for directions for coating metals with iron, cobalt, 
platinum, and various patinas. 

In the same year, De Ruolz first succeeded in depositing 
metallic alloys — for instance, brass — from the solutions of the 
mixed metallic salts. In 1843, the first use of thermo-electricity 
appears to have been made by Moses Poole, who took out a 
patent for the use of a thermo-electric pile instead of a voltaic 
battery for depositing purposes. 

From this time forward innumerable improvements in exist- 
ing processes were made ; and also the first endeavors to apply 
Faraday's discoveries to practical purposes. 

The invention of depositing metals by means of a permanent 
current of electricity obtained from steel magnets was perfected 
and first successfully worked by Messrs. Prime & Son, at their 
large silverware works, Birmingham. England, and the original 
machine constructed by Woolrych in 1844 — the first magnetic 
machine that ever deposited silver on a practical scale — is 
still preserved. It is now owned by the Corporation of Birm- 
ingham, England. The Woolrych machine stands 5 feet high, 
5 feet long, and 2J feet wide. 

As early as 1854, Christofle & Co. endeavored to replace 
their batteries by magnetic-electrical machines, and used the 
Holmes type, better known as the Alliance machine, which, 
•however, did not prove satisfactory; and besides, the prices of 
•these machines were, in comparison with their efficiency, exor- 
bitant. The machine constructed by Wilde proved objection- 
able on account of its heating while working, and the conse- 
quent frequent interruptions in the operations. 

In 1860 Dr. Antonie Pacinotti, of Pisa, suggested the use of 
•an iron ring wound around with insulated wire, in place of the 
cylinder. This ring> named after its inventor, has, with more 
or less modifications, become typical of many machines of 
modern construction. In the construction of all older ma- 
chines, steel magnets had been used, and their magnetism not 
being constant, the effect of the machine was consequently also 
not constant. Furthermore, they generated alternately nega- 



O ELECTRO-DEPOSITION OF METALS. 

tive and positive currents, which, by means of commutators,, 
had to be converted into currents of the same direction; and 
this, in consequence of the vigorous formation of sparks,, 
caused the rapid wearing-out of the commutators. 

These defects led to the employment of continuous mag- 
netism in the iron cores of the electro-magnets, the first 
machine based upon this principle being introduced in 1866,. 
by Siemens, which, in 1867, was succeeded by Wheatstone's. 

However, the first useful machine was introduced in 1871, 
by Zenobe Gramme, who in its construction made use of Paci- 
notti's ring. This machine was, in 1872, succeeded by Hefner- 
Alteneck's, of Berlin. In both machines the poles of the 
electro-magnet exert an inducing action only upon the outer 
wire wrappings of the revolving ring, the other portions being 
scarcely utilized, which increases the resistance and causes a 
useless production of heat. This defect led to the construction 
of flat-ring machines, in which the cylindrical ring is replaced 
by one of a flat shape and of a larger diameter, thus permitting 
the induction of both flat sides. Such a machine was, in 1874, 
built by Siemens & Halske, of Berlin; and in the same year by 
S. Schuckert, of Nuremberg. In Schuckert's machines nearly 
three-quarters of all the wire wrappings were under the induc- 
ing influence of both of the .large pole shoes of the electro- 
magnets. The flat-ring armature was later on replaced by the 
drum armature, and the more modern machines are almost 
without exception of the drum-armature type. 

By the construction of suitable dynamo-machines a mighty 
impetus was given to the electro-plating industry. They sup- 
planted the ordinary cell apparatus formerly used and ren- 
dered possible the production of electrolytically nickeled, 
coppered and brassed sheet-steel and tin-plate, as well as that 
of electrolytically zincked sheets, wire, building materials, etc. 
All these processes will be fully discussed, in the practical part, 
of this work. 



II. 

THEORETICAL PART. 



CHAPTER II. 

MAGNETISM AND ELECTRICITY. 

Magnetism. 

For the better understanding of the electrolytic laws it will 
be necessary to commence with the phenomena presented by 
magnetism, and to consider them somewhat more closely. 

A particular species of iron ore is remarkable for its prop- 
erty of attracting small pieces of iron and causing them to 
adhere to its surface. This iron ore is a combination of ferric 
oxide with ferrous oxide (Fe 3 4 ), and is called loadstone or 
magnetic iron ore. Its properties were known to the ancients, 
who called it magnesian stone, after Magnesia, a city in Thes- 
saly, in the neighborhood of which it was found. In the 
tenth or twelfth century it was discovered that this stone has 
the property of pointing north and south when suspended by 
a thread. This property was turned to advantage in naviga- 
tion and the term load stone (" leading stone ") was applied 
to the magnesian stone. If a natural loadstone be rubbed 
over a bar of steel, its characteristic properties will be com- 
municated to the bar, which will then be found to attract iron 
filings like the loadstone itself. The bar of steel thus treated 
is said to be magnetized, or to constitute an artificial magnet. 
The artificial magnets thus produced may be straight, in the 
shape of a horse-shoe, or annular ; but no matter what their 
form may be, there will always be two regions where the 

(9) 



10 ELECTRO-DEPOSITION OF METALS. 

attractive force reaches its maximum, while between these 
two points there is a region which has no attractive effect 
whatever upon iron filings. The two ends of the magnet, 
especially, show the greatest attractive force, and they are 
called the magnetic poles, whilst the line running around the 
magnet, which possesses no attractive force, is termed the 
neutral line or neutral zone. In a closed magnet the poles are 
situated on the ends of one and the same diameter, while the 
neutral zones are located on the ends of a diameter standing 
perpendicular to the first. 

When a magnetized bar or natural magnet is suspended at 
its center in any convenient manner, so as to be free to move 
in a horizontal plane, it is always found to assume a particular 
direction with regard to the earth, one end pointing nearly 
north and the other nearly south. If the bar be removed from 
this position it will tend to reassume it, and after a few oscilla- 
tions, settle at rest as before. The direction of the magnetic 
bar, i. e., that of its longitudinal axis, is called the magnetic 
meridian, while the pole pointing toward the north is usually 
distinguished as the north pole of the bar, and that which 
points southward as the south pole. 

A magnet, either natural or artificial, of symmetrical form, 
suspended in the presence of a second magnet, serves to ex- 
hibit certain phenomena of attraction and repulsion, which 
deserve particular attention. When a north pole is presented 
to a south pole, or a south pole to a north pole, attraction en- 
sues between them, the ends of the bar approaching each 
other, and, if permitted, adhering with considerable force. 
When, on the other hand, a north pole is brought near a sec- 
ond north pole, or a south pole near another south pole, 
mutual repulsion is observed, and th-e ends of the bar recede 
from each other as far as possible. Poles of an opposite name 
attract, and poles of a similar name repel each other. 

According to Ampere's theory, each molecule of iron or 
steel has a current of electricity circulating round it ; previous 
to magnetization these molecules — and hence the currents — 



MAGNETISM AND ELECTRICITY. 11 

are arranged irregularly ; during magnetization they are 
made to move parallel to one another, and as the magnetiza- 
tion becomes more perfect they gradually assume greater 
parallelism. 

If an iron or steel needle be suspended free in proximity to 
a magnet it assumes a fixed direction according to its greater 
or smaller distance from the poles or from the neutral zone. 
However, before the needle assumes this direction, it swings 
rapidly with a shorter stroke, or slowly with a longer stroke, 
according to the greater or smaller attractive force exerted 
upon it. The space within which the magnetic action of a 
magnet is exercised is called the magnetic field, and the mag- 
netic, as well as the electric, attractions and repulsions are, 
according to Coulomb, as the densities of the fluids acting upon 
each other, and inversely as the square of their distance. 

As electro-magnets act in exactly the same manner as mag- 
nets, their further properties will be discussed in the next 
section. 

Electro-Magnetism.. 

When a wire through which a current is passing is brought 
near, and parallel, to a magnetic needle, the latter is deflected 
from its ordinary position, no matter whether the current- 
carrying wire be placed alongside, above, or beneath it. The 
deflection of the needle is always in .the same direction, i. e., 
its north pole is always deflected in one and the same direction. 

The direction of the deflection is determined by what is 
known as Ampere's rule, which is as follows : Suppose an ob- 
server swimming in the direction of the current, so that it 
enters by his feet and emerges by his head : if the observer 
has his face turned towards the needle, the north pole is always 
deflected to his left. 

When the current-carrying wire is coiled in many windings 
around the needle, the action of the current is increased, be- 
cause every separate winding deflects the north pole in the 
same direction. Such instruments are known'as multipliers, or 



12 ELECTRO-DEPOSITION OF METALS. 

galvanoscopes, or galvanometers, and are used for recognizing 
feeble currents. These instruments have been improved by 
Nobili through the use of a very long coil of wire, and by the 
addition of a second needle. This instrument is known as the 
astatic galvanometer. The two needles are of equal size and 
magnetized as nearly as possible to the same extent. They 
are then immovably fixed together parallel and with their 
poles opposed, and hung by a long fiber of twisted silk, with 
the lower needle in the coil and the upper one above it. The 
advantage thus gained is twofold : The system is astatic, un- 
affected, or nearly so, by the magnetism of the earth ; and the 
needles being both acted upon in the same manner by the 
current, are urged with much greater force than one alone 
would be, all the actions of every part of the coil being strictly 
concurrent. A divided circle is placed below the upper needle, 
by which the angular motion can be measured, and the whole 
is inclosed in glass, to shield the needles from the agitation of 
the air. 

The deflection of the magnetic needle by the electric current 
has led to the construction of instruments which allow of the 
intensity of the current being measured by the magnitude of 
the deflection. Such instruments are, for instance, the tangent 
galvanometer, the sine galvanometer, etc., but they are almost 
exclusively used for scientific measurements, while for the de- 
termination of the intensity of current for electro-plating pur- 
poses other instruments are employed, which will be described 
later on. However, the electric current exerts not only a re- 
flecting action on magnetic needles, but is also capable of pro- 
ducing a magnetizing effect on iron and steel. If a bar of iron 
be surrounded by a coil of wire covered with silk or cotton for 
the purpose of insulation, it becomes magnetic so long as the 
current is conducted through the coil. Such iron bars con- 
verted into temporary magnets by the action of the current 
are called electro-magnets, and they will be the more highly 
magnetic, the greater the number of turns of the coil, and the: 
more intense the current passing through the turns. 



MAGNETISM AND ELECTRICITY. 



13 



The magnitude of the magnetizing force of the current is 
•expressed by the product from the number of turns and cur- 
rent-strength passing through the turns, and is called ampere- 
turn number. 

By interrupting the current passing through the wire-turns, 
the magnetism of the iron bar disappears to within a very 
small quantity, its magnitude depending on the quality of the 
iron. This remaining magnetism is called remanent or residual 
magnetism. 

An electro-magnet possesses the same properties as an ordi- 
nary magnet, and, like it, has a north pole and a south pole, 



Fig. 1. 



/ / ' 



/ 



/ 



s 






\ 



/ / / 







as well as a magnetic field, through which its influence ex- 
tends. Place a piece of paper above an electro-magnet and sift 
uniformly iron filings over it. On giving the paper slight 
taps, the filings arrange themselves in regular groups and 
lines. Most of the filings collect on the two poles, while, in 
fixed decreasing proportion^, lines of filings are formed from 
the north pole to the south pole. This experiment demon- 
strates that the action is strongest on the poles, and decreases 
towards the center. The entire space in which the magnetic 
action — the flow of the magnetic lines of force — exerts its influ- 
ence is called the magnetic field. The lines of force flow from 
the north pole to the south pole, where they combine, and flow 



14 ELECTRO-DEPOSITION OF METALS. 

back through the iron bar to the north pole, as shown in the 
accompanying illustration, Fig. 1. 

The dotted lines also take actually their course from one 
pole to the other, but by a more circuitous way. The direc- 
tion, as well as the magnitude, of the field force (see later on) 
varies on all points of the magnet or electro-magnet, with the 
sole exception of the symmetrical plane between the two poles, 
the latter being on all points struck at right angle by the lines 
of force. 

By placing a bar of soft iron, a b, in the proximity of a mag- 

Fig. 2. 




/^/VM;-ii;.i\ivv\-;//////';;-ij»\\\ N o* \ \ 



net or electro-magnet N S, covering both with a sheet of paper 
and sifting iron filings upon the latter, delineations, as shown 
in Fig. 2, are obtained. 

The lines of force gravitate in large numbers towards the 
side where the iron bar is, traverse the iron quite compactly, 
and while, without the bar, the center of the magnet showed a 
feeble magnetic field, the field-force in that place has now 
become greater. Upon the opposite side the density of the 
lines of force which pass through the air is less. The prop- 
erty of a material to be traversed by the lines of force is called 
its permeability. 

The number of lines of force which traverses through 1 



MAGNETISM AND ELECTRICITY. 15 . 

square centimeter of cross-section of a material, is called the 
magnitude of the magnetic induction of the material in question. 

Eyery material opposes a certain fixed resistance to the 
electrical current, as well as to the magnetic lines of force. 
Soft iron opposing the least resistance to the lines of force, it 
is most compactly traversed by them. Air, on the other 
hand, opposes far greater resistance, and, hence, the density of 
the lines of force, in Fig. 2, where they pass through the air 
is much less. 

A conducting wire through which passes a powerful current 
also becomes itself magnetic. If a circular conducting wire, 
through which a current passes, be suspended so as to move 
free around its vertical axis, its direction is influenced by the 
terrestrial magnetism, and it assumes such a position that its 
plane stands at a right angle upon the plane of the magnetic 
meridian. By now conducting the current through a spiral 
wire suspended free — a so-called solenoid — the plane of each 
separate turn will also place itself at a right angle upon the 
plane of the magnetic meridian, or in other words, the axis of 
the solenoid will be brought to lie in the magnetic meridian. 

In a manner similar to the action upon a magnet by a con- 
ducting wire through which a current passes, two conducting 
Wires, through which currents pass, exert attracting and re- 
pelling influences one upon the other. Two currents running 
parallel alongside each other in the same direction attract, 
but repel, each other, when running in opposite directions. 

Induction. 

By induction is understood the production of an electric 
current in a closed conductor which is in the immediate 
proximity of a current-carrying wire. 

Suppose we have two insulated copper-wire coils, a and b, 
Fig. 3, b being of a smaller diameter and inserted in a. 
When the two ends of b are connected with the poles of a 
battery, a current is formed in a the moment the current of 
b is closed. This current is recorded by the deflection of the 



16 



ELECTRO-DEPOSITION OF METALS. 



magnetic needle of a multiplier, M, which is connected with 
the ends of a, the deflection of the needle showing that the 
current produced in a by the current in b moves in an oppo- 
site direction. The current in a, however, is not lasting, 
because, after a few oscillations, the magnetic needle of the 
multiplier returns to its previous position and remains there, 
no matter how long the current may pass through b. If, 
however, the current in b be interrupted, the magnetic needle 
swings to the opposite direction, thus indicating the formation 

Fig. 3. 




•of a current in a, which passes through it in the same direc- 
tion as the interrupted current in b. 

The current causing this phenomenon is called the primary, 
inducing or main current, and that produced by it in the 
closed circuit, the secondary, induced or induction-current. From 
what has been above said, it is. clear that an electric current at 
the moment of its formation induces in a contiguous closed circuit 
a current of opposite direction, but when interrupted, a current of 
the same direction. 

In the same manner as closing and opening the main cur- 



MAGNETISM AND ELECTRICITY. 17 

rent, its sudden augmentation also effects the induction of a 
current of opposite direction in a contiguous wire, while its 
sudden weakening induces a current of the same direction. 
The same effect is also produced by bringing the main current- 
carrying wire closer to, or removing it further from, the con- 
tiguous wire. 

It is supposed that by closing the current a magnetic field is 
formed in the coil b, which sends forth its lines of force radially 
in an undulating motion. The lines of force cut. the turns of 
the coil, a, which is without current, and thereby induces a 
current. This current disappears again when the primary 
current flows in equal force, and re-appears when by the 
strengthening of the inducing current a change in the number 
of lines of force takes place by reason of the strengthening of 
the magnetic field. In the same manner induced currents are 
also produced by a decrease in the number of lines of force, 
and hence it follows that the production of induction-currents 
is always conditional on the change of proportion between the 
conductor and the magnetic field. 

When a magnet or electro-magnet is pushed into a wire coil, 
an electric current is produced in the turns of the coil so long 
as the motion of the magnet is continued; when the motion is 
interrupted, the production of current ceases. If the magnet 
be now withdrawn from the coil, a current is. again formed, 
which, however, flows in an opposite direction to that formed 
by pushing the magnet into the coil. The currents produced 
in the above-mentioned manner are also induction-currents, 
•and their formation is again explained by the fact that the 
lines of force cut the turns of the conducting wire, and excite 
thereby a current, the electro-motive force of which increases 
•or decreases with the magnitude of the number of lines of 
force. 

The induced currents follow the law of Ohm (see later on) 

in precisely the same manner as the inducing currents. A 

long induction-wire with a small cross-section offers greater 

resistance than a short wire with a larger cross-section, and 

2 



18 



ELECTEO-DEPOSTTION OF METALS. 



consequently, in the first case, the current will be of slighter 
intensity and higher electro-motive force, and, in the other, of 
greater intensity and less electro-motive force. 

Electro-magnetic alternating actions are the relations which 
exist between the magnetic field, the conductor, and the 
motion. The direction of the induced current can readily be 
followed by Fleming's hand rule, which is as follows : Hold 
the thumb and the first and the middle fingers of the right 
hand as nearly as possible at right angles to each other, as 
shown in Fig. 4, so as to represent three rectangular axes in. 
space. If the thumb points in the direction of motion, and. 

Fig. 4. 




the forefinger points along the direction of the magnetic lines,, 
then the middle finger will point in the direction of the in- 
duced electro-motive force. 

The mechanism of the formation of the electric current will 
be fully discussed later on, but it will be necessary to here 
give the values in which the performances of the current are 
expressed in order to shape the succeeding chapters more uni- 
formly. 

Fundamental Principles of Electro-Technics. 

Electric Units. For the better comprehension of the prop- 
erties, effects, and value of the electric current, it has become- 



MAGNETISM AND ELECTRICITY. 



19 



customary to compare it with a current of water, and this cus- 
tom will here be followed. 

Fig. 5 shows a funnel A secured in the stand D, and con- 
nected by a tube with the horizontal discharge pipe B. 
Underneath B stands the vessel C, which serves for catching 
the water. If the funnel be placed in a higher position and 
filled with water, the latter runs off more rapidly from the 
pipe B, than when the funnel occupies a lower position. If 

Fig. 5. 




the force of the current of water is expressed according to the 
quantity of water which runs out in the time-unit, it follows 
that in a certain pipe conduit, the quantity of water which 
runs out in the time-unit, increases if there be an increase in 
the height of fall. 

Suppose it has been determined how many seconds are re- 
quired for the water in the funnel to run through the pipe B. 
If the pipe be now lengthened by joining to it several pipes of 



20 ELECTKODEPOSITION OF METALS. 

the same cross-section, it will be found that a greater number 
of seconds are required for emptying the funnel than with the 
use of only one pipe. From this we learn that with a deter- 
mined height of fall, the quantity of water which flows in the 
time-unit through a pipe of determined cross-section decreases 
when the pipe is lengthened. 

If now the discharge pipes used in the last experiment be 
replaced by pipes of the same length but of smaller cross- 
sections, it will be found that a greater number of seconds are 
also required for emptying the funnel than with the use of 
pipes of larger cross-sections. Hence, at a determined height 
of fall, the quantity of water which flows through a pipe of 
fixed length in the time-unit, decreases if the cross-section of 
the pipe be increased. 

The height of fall has to be considered as the motive power 
which effects the flow of water. The pipe opposes a resistance 
to the flowing water, this resistance increasing with the length 
of the pipe and the reduction of the cross-section, and decreas- 
ing as the cross-section becomes larger. 

If now these principles be applied to the electric current, by 
current-strength has to be understood the quantity of electricity 
which passes in the time-unit through a conductor. 

The unit of the quantity of electricity is called the coulomb. 
Its magnitude results from the fact that for the 1 gramme 
hydrogen 96,540 coulombs must migrate through the elec- 
trolyte. 

The unit of current-strength is called the ampere, i. e., a cur- 
rent which every second carries one coulomb through the con- 
ductor. The magnitude of an ampere is the current-strength 
which is capable of separating in one minute 0.01973 gramme 
of copper, or in one hour 1.184 grammes, from a cupric sul- 
phate solution. In order to separate from an electrolyte 1 
gramme of hydrogen, a current of 1 ampere must accordingly 
pass 96,540 seconds, or 26 hours 49 minutes, through the 
electrolyte. 

The electro-motive force or tension of the electric current cor- 



MAGNETISM AND ELECTRICITY. 21 

responds to the height of fall of water. The work an electric 
current is capable of performing does not only depend on the 
current-strength, i. e., the quantity of current, which passes 
in the time-unit through a cross-section of the conductor, but 
also on the electro-motive force. The unit of electro -motive force 
is called the volt. The material value of a volt is about the 
electro-motive force of a Daniell's cell (zinc-copper). 

In a water conduit the difference in pressure between two 
points in the pipe is measured according to the difference in 
the height of the column of water. To this difference in pres- 
sure corresponds the difference of electro-motive force, also called 
difference of potential, which is expressed by the number of 
volts. 

The product of current-strength in amperes and electro- 
motive force in volts, which, in so far as an ampere is an 
electric unit in one second, represents work performed in one 
second, is called the volt-ampere or watt, and hence is the unit 
of electrical work. 

The electric resistance is similar to the resistance offered by 
a water-pipe to the flowing water. As previously stated, the 
quantity of water running out in the time-unit decreases when 
the pipe is lengthened, as well as when the cross-section is 
smaller, and, in both cases, the resistance opposed to the water 
by friction increases. On the other hand, the quantity of 
water flowing out in the time-unit increases, when the length 
of pipe is shortened and the cross-section increased, because 
there is less resistance. The same takes place with the electric 
current. The quantity of current which can pass through a 
conductor becomes smaller when the length of the conductor 
is increased and its cross-section reduced, because the resist- 
ance becomes thereby correspondingly greater. It has further 
been seen that the quantity of flowing water in a certain con- 
duit increases as the height of fall becomes greater. If now 
the electro-motive force of the electric current be substituted 
for the height of fall, the current-strength which passes through 
a conductor will be increased in keeping with the changing 



22 ELECTRO-DEPOSITION OE METALS. 

electro-motive force. From this results the following propo- 
sition : 

In a determined circuit the current-strength increases at the 
same ratio as the electro-motive force which acts upon the circuit. 

If now the current-strength increases proportionally to the 
electro-motive force, the expression, 

E(= electro-motive force in the circuit) 
J (= current-strength in the circuit), 
must be a fixed value dependent on the magnitude of the 
electro-motive force and the current-strength, and this value is 
called the electric resistance of the circuit. 

. The unit of electric resistance is called the ohm, it having thus 
been named after the physicist Ohm, who laid down the rules 
known as the laws of Ohm. The value of the ohm is equal to 
the resistance at 0° C. of a column of mercury of one square 
millimeter section and one meter long. A volt is the electro- 
motive force which is capable of sending a current-strength of 
one ampere through the resistance of one ohm. 

Law of Ohm. It has above been seen that the fraction 

K 

(1) - = resistance (W), 
u 

whereby under E is understood the electro-motive force which 
is at disposal in the entire circuit. The current-strength J is 
throughout in all places of the same magnitude, and W indi- 
cates the total resistance of the circuit. 

From the preceding equation are deduced the following 
further equations : 

(2) W. J=E, 
that is, the electro-motive force is equal to the product of 
current-strength and resistance ; 

that is, the current-strength is equal to the electro-motive 
force divided by the resistance. 

Example to equation 1. If through a circuit closed by a long 



MAGNETISM AND ELECTRICITY. 23 

wire and a current-meter, a current of 4 volts and 2 amperes 
is conducted, the resistance of the circuit is 

4 volts = 2 ohms. 
2 amperes 

Example to equation 2. 5 amperes are to be conducted 
through a circuit of 1 ohm resistance, what electro-motive 
force is required for the purpose? 

1 ohm X 5 amperes = 1 volt. 

Example to equation 3. A current of 10 volts electro-motive 
force is to be conducted through a circuit with 2 ohms resist- 
ance ; what current-strength may be looked for? 

JO volts K 

= o amperes. 

2 ohms 

The total resistance, W, is composed of the internal resist- 
ance of the current-source and the external resistance which the 
•current in its progression has to overcome. This external re- 
sistance is composed of the resistance of the conducting wire, 
the electrolyte, etc. If the internal resistance be designated 
W and the external resistances wl and w2, equation 3 assumes 
the following aspect : 

E 

(4) - ^J 

w W + wl + w2 J - 

Hence, the current-strength is equal to the total electro- 
motive force divided by the sum of the internal and external 
resistances. 

Example to equation If.. A cell possesses an internal resist- 
ance of 0.3 ohm and an electro-motive force of 1.8 volts, and 
the resistance of the conducting wire, wl, is 1 ohm and that 
of the electrolyte 0.5 ohm. The current-strength then amounts 



tolamp^re( a3+ 1 1 8 +a5 = l). 



If a determined current-strength flows through a resistance, 
■a decrease of electro-motive force results in the resistance, ex- 
actly as in a water-conduit the pressure of the column of water 
is decreased with the length of the pipe, a decrease in pressure 
taking place. It might be said that the resistance consumes 



24 ELECTRO-DEPOSITION OF METALS. 

the pressure, and the greater the resistance of a conductor is,, 
the less the current-strength will be, since, if in the equation 3 
the divisor grows, the current-strength, J, must become less. 
According to the law of Ohm, the following proposition here 
holds good : 

The current-strength is inversely proportional to the sum of {he- 
resistance of the circuit, or, in other words, the current-strength 
decreases in the proportion as, with the same electro-motive 
force, the resistances increase. 

The resistance of a wire or of a body increases in proportion 
to its increase in length, and decreases in proportion to the in- 
crease of its cross-section. If the resistance of a conductor be 
designated W, its length L, and its cross-section Q, then 

(5) W = - 

The decreasing electro-motive force, according to the law of 
Ohm, is calculated by the following equation, in which a 
denotes the decrease in electro-motive force, J the qurrent- 
strength, Wi the internal resistance. 

(6) a = J X Wi. 

In the example to equation 4, the current-strength amounted 
to 1, and the internal resistance of the element to 0.3 ohm; 
this gives a decrease of electro-motive force of 1 x 0.3 = 0.3 
volt; hence the actual electro-motive force of the current flow- 
ing from the cell will only be: E — a = 1.8 — 0.3 == 1.5 volts, 
and this effective electro-motive force is called the impressed 
electro-motive force of the cell or other source of current. 

If now the preceding separate propositions of the law of 
Ohm be collected, the latter reads as follows: 

The current-strength is directly proportional to the sum of the 
electro-motive forces, and inversely proportional to the resistance 
of the circuit ; however, the resistance of each part of the circuit 
is proportional to its length, and inversely proportional to its cross- 
section. 

Specific resistances. The resistance of a wire of the same 
material is consequently proportional to its length and in- 



MAGNETISM AND ELECTRICITY. 25- 

versely proportional to its cross-section. If now, one after the 
other, wires of equal length and equal cross-section, but of 
different materials, be placed between the binding posts of a 
source of current, different current-strengths are obtained in 
the wires. From this it follows that every material jDOssesses 
a definite capacity of its own to conduct the current. Hence, 
if the resistance is to be calculated from the length of the wire 
and its cross-section, the magnitude, called the specific resist- 
ance of the material, has to be taken into consideration. By 
the specific resistance is to be understood for conductors of 
the first class, the resistance of a material 1 meter in length 
and 1 square millimeter cross-section, and for conductors of 
the second class, the resistance of a cube of fluid of 10 centi- 
meters = 1 decimeter side length. 

If the specific resistance be denoted c, the resistance of a 
wire of L meters length and a cross-section of Q square milli- 
meters cross-section is found from the equation : 

(7)W=|.c. 

The specific resistance c of the metals at 59° F., and the co- 
efficient of temperature a (see later on) amount to for : 



Aluminium . 
Antimony . . 
Bismuth . . 
Brass .... 
Copper . . . 
German silver 
Gold ...'.. 
Iron .... 
Lead .... 
Manganin . . 
Mercury . . 
Nickel . . . 
Xickelin . . . 
Platinum . . 
Silver . . . . 
Steel ....'. 
Tin .... . 
Zinc . . . - 



c. 


x a ' 


0.029 


0.0039 


0.475 * 


0.0041 


1.250 


0.0037 


0.10 to 0.071 


0.0016 


0.017 


0.0041 


0.30 to 0.18 


0.0003 


0.024 


0.0040 


0.120 to 0.10 


0.0048 


0.207 


0.0039 


0.455 


0.00002 


0.953 


0.0009 


0.15 


0.0036 


0.435 to 0.340 


0.000025 


0.15 to 0.094 


0.0024 


0.016 


0.0038 


0.50 to 0.168 


0.0040 


0.10 


0.0042 


0.065 


0.0040 



■26 ELECTRO-DEPOSITION OF METALS. 

From the above table it will be seen that silver is the best 
conductor, then copper, the specific resistance of which is 
slightly greater, next gold, aluminium, and so on. The great- 
est specific resistance in descending series have mercury, man- 
ganin, nickelin, German silver, these metals or metallic alloys 
showing at the same time the slightest change in resistance at 
a higher temperature. 

Coefficient of temperature. One and the same material has 
the same specific resistance only at the same temperature. In 
•conductors of the first class — the metals — the resistance in- 
creases, though even only in a slight degree, as the tempera- 
ture increases. The formula for this is : 

(8)Wt 2 =.Wt, [+a(t 2 — t,)], 
in which Wt 2 is the resistance at the higher temperature t 2 , 
and Wtj, the resistance at the lower temperature t x , and the 
magnitude a, the number of ohms the resistance increases by 
a rise of 1° C. in the temperature. 

In the conductors of the second class — the electrolytes — the 
resistance decreases, as a rule quite considerably with a rise 
in the temperature, and is calculated from the following 
equation : 

(9) Wt 2 =-Wt 2 [1— a (t 2 — 10]. 

The magnitude a is called the coefficient of temperature of 
a material, and these coefficients are given in the second 
column of the above table. 

Law of Kirchhoff. From a water-conduit, the water may 
•by means of branch-pipes be conducted to different points. 
In the same manner, the electric current may be conducted 
from the main wire by means of different wires to different 
places. This is called branching or distributing the current. 
The wire from the source of current up to the point of branch- 
ing is known as the main wire and the wires branching off as 
branch wires. 

The heavy lines in Fig. 6 represent the main wires ; a is the 
.junction from which three wires, 1, 2, and 3, branch off, and b, 
■the. junction at which they meet. If a current-meter (see later 



MAGNETISM AND ELECTRICITY. 



27 



on) be placed in the main wire, and one in each of the branch 
wires, it will be found that the sum of the current-quantities 
flowing through the separate branch wires is equal to the 
current-quantity in the main wire. If, however, the current- 
quantities which flow through the separate branch wires of 
the same cross-section, 1, 2, 3, are examined, it will be seen 
that these current-quantities are not the same, but vary one 
from the other, the current-quantity flowing in the branch 
wire 1 being greater than that in 2 or 3, while that in 2 is 
greater than that in 3. These variations are due to the fact 

Fig. 6. 




that the branch wire 1 is shorter than 2 or 3, and hence pos- 
sesses less resistance. Suppose that the longest branch-wire, 
3, had a much larger cross-section than the branch-wires 1 
and 2. By reason of its slighter resistance more current 
would flow through it, notwithstanding its length, than 
through 1 and 2. 

Hence the law of Kirchhoff may be summed up as follows : 

1. When the current is branched the sum of the current-strengths 
in the separate branch wires is exactly as great as the current- 
strength before and after branching off. 

2. The current-strengths in the separate branch-idres distribute 
themselves in inverse proportion to 'their resistances. 

In the practical part of this work the further conclusions 
resulting from the law of Kirchhoff will be referred to. 



28 ELECTRO-DEPOSITION OF METALS. 

Law of Joule. — If a current flows through a conductor 
which possesses not too slight a resistance, the latter becomes 
heated, and, hence, electric energy is converted into heat. It 
has been shown by experiments that the quantity of heat, 
which is produced by the passage of a determined current- 
strength through a determined resistance, increases in the 
same ratio as the duration of the passage of the current. It 
has also been shown that by the passage of a determined 
current-strength through a resistance, the heat produced in 
the latter in a determined time is proportional to the magni- 
tude of the resistance, and, hence, that the quantity of heat 
becomes larger as the resistance increases. It has further 
been, established that the quantity of heat produced in a de- 
termined resistance during a determined space of time by the 
current flowing through it, is proportional to the square of 
the current strength. 

From these propositions determined by experiments, the 
law of Joule may be brought into the formula : 

(10) Q = C. J 2 . W. t. 

If Q is the quantity of heat developed in calories, J is the 
current-strength in amperes which flows through the resist- 
ance, W the resistance through which J flows, and t the space 
of time in seconds of the passage of the 'current ; C is a con- 
stant which by experiments has been ascertained as 0.0002392. 
In words, Joule's law, therefore, reads: The quantity of heat 
produced in t seconds by the passage of a current-strength J through 
the resistance W is proportional to the expression J 2 Wt. 

Frictional Electricity. 

In an ordinary state solid bodies exhibit no attractive effect 
upon such light particles as strips of paper, balls of elderpith, 
etc., but by being rubbed with a dry cloth or fur, many solid 
bodies acquire the property of attracting such light bodies as 
mentioned above. The cause of this phenomenon is called 
electricity, and the bodies which possess this property of be- 
coming electric by friction are termed idio-electrics, and those 



MAGNETISM AND ELECTRICITY. 29 

which do not appear to possess it, non-electrics. Gray, in 1727, 
found that all non-electric bodies conduct electricity, and hence 
are conductors, while those which become electric by friction 
are non-conductors of electricity. Strictly speaking, there are 
no non-conductors, because the resins, silk, glass, etc., conduct 
electricity, though only very badly. It is therefore better to 
distinguish good and bad conductors. To test whether a body 
belongs to the idio-electrics, the so-called electroscope is used, 
which in its simplest form consists of a glass rod mounted on a 
stand, and bent at the top into a hook, from which hangs by a 
silken thread or hair a pith ball. If, on bringing the rubbed 
body near the pith ball, the latter is attracted, the body is 
electric ; whilst if the ball is not attracted, the body is either 
non-electric, or its electricity is too slight, to produce an attrac- 
tive effect. 

From the following experiments it was found that there exist 
two kinds of electricity: When a rubbed rod of glass or shellac 
is brought near the ball of elder-pith suspended to a silk thread, 
the ball is attracted, touches the rod, adheres for a few moments, 
and is then repelled. This repulsion is due to the fact that the 
ball by coming in contact with the rod becomes itself electric, 
and its electricity must first be withdrawn by touching with 
the hand before it can again be attracted by the rod. By now 
taking two such balls, one of which has been made electric by 
touching with a glass rod, which had been rubbed with silk, 
and the other by touching with a shellac rod rubbed with cloth, 
it will be observed that the ball, which is repelled by the glass 
rod, is attracted by the shellac rod, and vice versa. These two 
kinds of electricity are called vitreous or positive, and resinous 
or negative electricity, and it has been found that electricities 
of a similar name attract, and electricities of an opposite name 
repel each other. 

Contact Electricity. 

However, a current of electricity is generated not only by 
friction, but also by the contact of various metals. In the 



30 ELECTRO-DEPOSITION OF METALS. 

same manner as the copper and iron in Galvani's experiments 
with the frog-leg, other metals and conductors of electricity 
also become electric by contact, the electric charges, being, 
however, stronger or weaker, according to the nature of the 
metals. If zinc be brought in contact with platinum, it be- 
comes more strongly positively electric than when in contact 
with copper ; whilst, however, copper in contact with zinc is 
negatively excited, in contact with platinum it becomes posi- 
tively electric. 

The metal which has become positively electric is said to 
have the higher potential, i. e., it possesses a larger measure of 
electricity than the metal which has become negatively elec- 
tric, and as the flow of water from higher to lower points 
takes place in a larger degree the greater the difference in 
altitude is, the electric current flows also the more rapidly 
from a positively charged body — the positive pole — to the 
negatively charged body — the negative pole — the greater the 
difference in their charges is, and this difference in the charges 
of two bodies is called difference of potential. 

If now the metals be arranged in a series so that each pre- 
ceding metal becomes positively electric in contact with the 
succeeding one, a series of electro-motive force is obtained in 
which the metals or conductors of electricity stand as follows: 
Potassium, sodium, magnesium, aluminium, zinc, cadmium, 
iron, nickel, lead, tin, copper, silver, mercury, gold, platinum, 
antimony, graphite. 

While two metals of the series of electro-motive force touch- 
ing each other become electrically excited in such a manner 
that one becomes positively and the other negatively electric, 
an exchange of the opposite electricities takes place by intro- 
ducing a conducting fluid between the metals. Thus, if a 
plate of zinc and a plate of copper connected by a metallic 
wire are immersed in a conducting fluid, for instance, dilute 
sulphuric acid, the electricity of the positive zinc passes 
through the fluid to the negative copper, and returns through 
the wire — the closed circuit — to the zinc. However, in the 



xMAGNETISM AND ELECTRICITY. 31 

same degree with which the electricities equalize themselves, 
new quantities of them are constantly formed on the points of 
contact of the metals with the conducting fluid ; and, hence, 
the flow of electricity is continuous. This electric current 
generated by the contact of metals and fluids is called the 
galvanic current; or, since it is generated by the intervention 
of fluid conductors, hydro-electric current. 

A combination of conductors which yield such a galvanic 
current is called a galvanic or voltaic cell or battery, and the 
production of current from the above-mentioned differences of 
potential of the metals was formerly explained by the suppo- 
sition that chemical processes take place in the solutions in 
which the metal plate is immersed. However, as will be seen 
later on, the production of the current is at present reduced, 
according to Nernst's theory, to the solution-pressure and tho 
osmotic pressure. It is first of all necessary to explain the 
fundamental chemical principles, since without a knowledge 
of them, the subsequent sections could not be understood. 

Fundamental Chemical Principles. 

The phenomena presented by magnetism and electricity 
have, so far as required for our purposes, been briefly discussed 
in the preceding sections. All these phenomena, no matter 
how much they may vary in their nature, have this in com- 
mon, that the bodies in which they appear undergo no change 
in substance and weight, notwithstanding that they acquire 
the most diverse properties. If, for instance, steel by being 
rubbed with a magnet has acquired the power of attracting 
iron articles, and hence has become a magnet itself, no other 
changes can be noticed in it, even by .the most minute ex- 
amination ; it remains the same steel which had been origin- 
ally used, it having solely acquired the property of being 
capable of acting as a magnet. 

The phenomena to be treated of in this section devoted to ' 
the fundamental chemical principles, are of an entirely dif- 
ferent nature, we having constantly to deal with changes in 
substance, as may be shown hy the following examples. 



•32 ELECTRO-DEPOSITION OF METALS. 

When bright iron or steel is exposed to the action of moist 
air, it becomes gradually coated with a brown-red powder 
known as rust, which is formed by the iron combining with 
the oxygen of the air. On examining this brown-red sub- 
stance it will be found to possess entirely different properties 
from iron, and that the latter has undergone a material change. 
By the absorption of oxygen the iron has been converted into 
an oxide of iron, and a process known as a chemical process 
has taken place, whereby from two different substances a third 
one is formed which possesses other properties, and is of a 
•different composition. 

The phenomena which appear in subjecting the well-known 
red oxide of mercury or red precipitate to the action of heat, 
furnish another example of a chemical process. If red oxide 
of mercury be heated in a test-tube, its red color soon dis- 
appears, its bulk decreases, and, if heating be for some time 
continued, it disappears entirely. On the other hand, there 
will be found deposited upon the upper, cooler portions of the 
tube, metallic mercury in its characteristic form of globules. 
If the gaseous products evolved during the process be also 
caught, a gas, different in its nature from air, is obtained, 
which will inflame a mere spark on wood. This gas is the 
well-known oxygen, which plays such an important part in the 
respiratory process of human beings and animals. 

While by the formation of a new body in consequence of 
the combination of different substances, the first example 
presents a chemical process of a synthetic, i. e., building-up, 
nature, the second one, shows a process of an analytical, i. e., 
resolving, nature. We have thus learned the nature of the 
chemical processes in general, which, no matter how diverse 
the separate processes may be, consist, in that an alteration in 
the material nature of the bodies takes place. If the quanti- 
ties by weight of a substance entering into a chemical change 
be determined, it will be noticed that in all transpositions, in 
the decomposition of a compound into its constituents, and in 
the union of the elements to form compound bodies, loss in 



MAGNETISM AND ELECTRICITY. 66 

weight never occurs. The weight of the resulting compound is 
invariably equal to the sum of the weight of the bodies entering 
into the reaction. This furnishes proof that the most import- 
ant law of the indestructibility and non-creation of weighable 
substance in nature, which is known as the law of the conserva- 
tion of matter, is also valid as regards chemical processes. 

Moreover, we find the further conformity to law that the 
•quantities by weight of the substances formed by their mutual 
-action in a chemical process, stand one to the other in a fixed, 
unchangeable proportion. Thus, for instance, a given quan- 
tity by weight of iron can only combine, under the co-opera- 
tion of water, with an unchangeable quantity of oxygen, to 
ferric hydroxide (rust) ; and the quantities by weight of 
mercury and oxygen formed from red oxide of mercury, 
must always stand one to the other in an unchangeable pro- 
portion. 

If now in a similar manner as in the second example, all 
the bodies offered by nature be decomposed by means of the 
auxiliary agents at our command, into such constituents as do 
not allow of a division into further substances, it will be found 
that there are altogether comparatively few substances which 
•compose the bodies of nature. Such substances are called 
■chemical elements ; they cannot be converted into each other, 
but constitute, as it were, the limit of chemical change. At 
present 79 such elements are known. 

The smallest portion of an element, or of a chemical com- 
pound, which can exist in a free state, is called a molecule. If, 
for instance, common salt be triturated to such a fine powder 
that further reduction by mechanical means is impossible, such 
finest particle represents the molecule. However, common 
salt consists of two elements, namely, sodium and chlorine. 
Consequently both these elements must be present in the mole- 
cule, and these smallest particles of the elements, which are 
contained in the molecule, are called atoms. Hence the atom 
of an element is the smallest quantity of it which takes part in 
•chemical combinations. As a rule, the atom is equal to half 
3 



34 ELECTRO-DEPOSITION OF METALS. 

the molecule. Hence, for the formation of a molecule at least 
two atoms of an element are required. 

The atoms of the elements aggregate according to fixed pro- 
portions by weight, and the smallest quantities by weight of 
the elements which enter into combinations with each other 
are called their atomic weights, the weight of hydrogen, which 
is the highest of all the elements, being taken as the unit. It 
must, however, be stated that a series of elements may unite 
not only in a single proportion of weight, but also in several 
different ones, forming thereby combinations of entirely dif- 
ferent properties. If, however, these different proportions by 
weight are more closely compared, they will be found to stand 
in quite simple relations to each other, the higher being always- 
a simple multiple of the lowest. 

In the table below are given the most important chemical 
elements, together with their atomic weights. In addition the 
table contains the symbols used for designating the elements. 
These symbols are formed from the first letters of their names, 
derived either from the Latin or Greek. Hydrogen is, for in- 
stance, represented by the letter H, from the word Hydrogenium; 
Oxygen by 0, from oxygenium ; Silver by Ag, from argentum. 
If Latin or Greek names of several elements have the same 
first letters, the latter serves only for the designation of one of 
these elements, while for the other elements, the first letter is 
furnished with an additional characteristic letter. Thus, for 
instance, boron is represented by the letter B ; barium by Ba ; 
bismuth by Bi ; bromine by Br. 



MAGNETISM AND ELECTRICITY. 



35 



International Table of the Atomic Weights of the Most Important 
Elements, (1911). 



Name of Element. 



Aluminium 
Antimony . 
Arsenic . . 
Barium . . 
Bismuth . 
Boron . . 
Bromine . 
Cadmium . 
Calcium . 
Carbon . . 
Chlorine . 
Chromium. 
Cobalt . . 
Copper . . 
Fluorine . 
Gold . . . 
Hydrogen . 
Iodine . . 
Iron . . . 



Symbol. 


Atomic 
Weight. 


Al 


27.1 


Sb 


120.2 


As 


74.96 


Ba 


137.37 


Bi 


208.0 


B 


11.0 


Bi- 


79.92 


Cd 


112.40 


Ca 


40.09 


C 


12.0 


CI 


35.46 


Cr 


52.0 


Co 


58.97 


Cu 


63.57 


F 


19.0 


Au 


197.2 


H 


1.008 


I 


126.92 


Fe 


55.85 



Name of Element. 



Lead . . . . 
Magnesium . 
Manganese . 
Mercury . . 
Nickel . . . 
Nitrogen . . 
Osmium . . 
Oxygen . . . 
Phosphorus , 
Platinum . . 
Potassium . . 
Selenium . . 
Silicon . . . 
Silver . . - 
Sodium . . . 
Sulphur . . 
Tin . . . . 
Zinc .... 



Symbol. 



Pb 
Mg 

Mn 
Hg 

Ni 
N 
Os 
O 
P 
Pt 
K 
Se 
Si 
Ag 
Na 
S 

Sn 
Zn 



Atomic 
Weight. 



207.10 
24.32 
54.93 

200.0 
58.68 
14.01 

190.9 
16.00 
31.04 

195.2 
39.10 
79.2 
28.3 

107.88 
23.00 
32.07 

119.0 
65.37 



The symbols not only represent the elementary bodies, but 
also their fixed quantities by weight, so that, for instance, the 
symbol Ni means 58.68 parts by weight of nickel. 

Compounds produced by the union of the elements are 
represented by placing their corresponding symbols together 
and designating them chemical formulas. As previously men- 
tioned, common salt consists of one atom sodium (Na) and 
one atom chlorine (CI), and hence its formula has to be written 
NaCl. The latter shows that one molecule of common salt 
consists of 23.00 parts by weight of sodium and 35.46 parts by 
weight of chlorine, which together form 58.46 parts by weight 
of common salt. If several atoms of an element are present 
in a compound, this is denoted by numbers which are written 
to the right of the symbol, below, as proposed by Poggendorf, 
or above, as proposed by Berzelius, and still used at the pres- 
ent by a few people. Water, for instance, contains 2 atoms 
hydrogen (H) and one atom oxygen (O), and hence its formula 



36 ELECTRO-DEPOSITION OF METALS. 

is H 2 0, which indicates that 2 parts by weight of hydrogen, 
together with 16 parts by weight of oxygen, form 18.016 parts 
by weight of water. 

The symbols may be said to constitute the chemical alpha- 
bet and the formulas may be considered as the words of the 
chemical language. By means of the symbols and formulas 
it is made possible, to express in the most simple manner, the 
chemical processes by equations, which not only denote the 
manner of the chemical transposition, but also allow of the 
calculation of the quantities by weight, which have entered 
into reaction in the transposition of the different .substances. 
If, according to this our former examples, by means of which 
it has been endeavored to explain the nature of a chemical 
process, be translated into this chemical language, the equa- 
tions read as follows : 

1. 2Fe 2 + 30 2 + 6H 2 = 4Fe 3 (OH) 8 . 

Iron. Oxygen. Water. Ferric -hydroxide. 

2. 2HgO = Hg 2 + 2 . 

Mercuric oxide. Mercury. Oxygen. 

Valence of the elements. If the combinations into which the 
elements enter one with the other are more closely examined, 
and their formulas compared, it will be seen that entire groups 
of combinations are composed in an analogous manner. This 
analogy of composition appears very plainly in the compounds 
into which a series of elements enters with hydrogen, and we 
thus come across four different groups of compounds. The 
elements of the first group, namely, of the halogens, chlorine, 
bromine, iodine and fluorine, combine with one atom of 
hydrogen ; those of the second group, to which belong oxygen 
and sulphur, are capable of saturating two atoms of hydrogen ; 
those of the third group, which embraces nitrogen, phos- 
phorus, arsenic and antimony, fix three atoms of hydrogen, 
and finally, the elements of the fourth group, carbon and 
silicon, may combine with four atoms of hydrogen. Hence, 
we must ascribe a particular function of affinity to each ele- 



MAGNETISM AND ELECTRICITY. 37 

ment in its relation to hydrogen, and this property is called 
valence. 

Now, according as the elements are capable of combining 
with one, two, three or four atoms of hydrogen, they are 
designated as univalent, bivalent, trivalent, or quadrivalent ; 
and all elements, which possess the same valence, are called 
chemically equivalent. Tn chemical compounds, such equiv- 
alent elements may replace each other atom for atom, such 
substitution being also possible in elements of dissimilar val- 
ence, but it must take place in such a manner that a bivalent 
atom replaces two hydrogen atoms, a trivalent atom three 
hydrogen atoms, so that an equal number of valences is always 
exchanged. Thus, in accordance with this, one atom of 
chlorine is equivalent to one atom of hydrogen and hence, 
when a substitution of hydrogen by chlorine results, it can 
only be by one atom of chlorine taking the place of one atom 
of hydrogen. Hence it follows that 35.46 parts by weight of 
chlorine are equivalent to one part by weight of hydrogen. 
On the other hand, one atom of oxygen is equivalent to two 
atoms of hydrogen, or 16 parts by weight of the former are 
equivalent to 2 parts by weight of the latter. A mutual sub- 
stitution of these two elements must, therefore, always take 
place in the proportion of 16 to 2. Since the elements, nitro- 
gen, phosphorus, etc., are capable of fixing 3 hydrogen atoms, 
mutual substitution must also take place in such a man- 
ner that 1 nitrogen atom replaces 3 hydrogen atoms or that 

— ! — = 4.67 parts by weight of nitrogen are substituted for 1 
o 

part by weight of hydrogen. Finally, one atom of carbon or 

of silicon is equivalent to 4 parts by weight of hydrogen, or 

1 part by weight of hydrogen is replaced by 3 parts by weight 

of carbon. These quantities by weight determined for some 

of the elements, which are equivalent to 1 part by weight of 

hydrogen, or, in general, to one part by weight of a univalent 

element, are called equivalent weights or combining weights, and 

are in a similar manner deduced for all the other elements. 



38 ELECTRO-DEPOSITION OF METALS. 

While the elements preserve a constant valence towards 
hydrogen, many of them show a varying valence, which 
differs also from the hydrogen-valence towards other elements, 
so that, for instance, the same element may appear opposite to 
a second one, trivalent in one combination and quinquivalent 
in another. Combinations of phosphorus with chlorine may 
serve as an example. Together they form a combination, 
PC1 3 , as well as one PC1 5 ;-in the first case 3 atoms of chlor- 
ine or 3 X 35.46 parts by weight are equivalent to 1 atom of 
phosphorus or 31.04 parts by weight. This capacity of differ- 
ent elements of being endowed with totally unequal valence, 
forces us to the assumption that valence is not a characteristic 
property of the elements, but is dependent on the nature of the 
elements combining with each other, and is also influenced 
by the conditions under which the formation of the chemical 
combination takes place. 

By arranging the most important elements according to 
their valence, we obtain the following groups : 

Univalent elements: Hydrogen, chlorine, bromine, "iodine, 

fluorine, potassium, sodium, silver. 
Bivalent elements : Oxygen, sulphur, barium, strontium, 
calcium, magnesium, cadmium, zinc, lead, copper, 
mercury. 
Bivalent and trivalent elements: Iron, cobalt, nickel, man- 
ganese. 
Trivalent elements : Boron, aluminium, gold. 
Trivalent and quinquivalent elements : Oxygen, phosphorus, 

arsenic, antimony, bismuth. 
Quadrivalent elements: Carbon, silicon, tin, platinum. 
Later on", in the section on the fundamental principles of 
electro-chemistry, in speaking of the development of the laws 
of Faraday, these groups will have to be referred to, and their 
importance will then become evident. 

Metals and non-metals. In accordance with the greater or 
less conformity of their physical j^roperties, the elements have, 
for the sake of expediency, been sub-divided into two sections, 



MAGNETISM AND ELECTRICITY. 39 

namely, metals and non-metals, the latter being also called 
metalloids. The first section embraces the elements the prin- 
ciple characteristics of which are that they show metallic 
luster, are opaque or at the utmost translucent in thin laminae, 
are, as a rule, fairly malleable and ductile, and with the one 
exception of mercury, are all solid bodies at ordinary temper- 
atures and pressures, and are good conductors of heat and 
electricity. All the other elements which have not such 
physical properties in common are classed as metalloids. The 
two groups of bodies obtained by this mode of division also 
show in a chemical respect such similarities as to justify this 
classification, the metalloids forming with hydrogen readily 
volatile, mostly gaseous, combinations, while the metals unite 
more rarely with hydrogen, and, at any rate, do not form 
volatile combinations with it. The combinations which the 
metalloids form with oxygen also show, in their behavior 
towards water, very characteristic phenomena, entirely differ- 
ent from those presented by compounds of the metals with 
oxygen. These differences will later on be referred to in de- 
tail. A very remarkable difference of the utmost importance, 
especially for our purpose, is in the action of the electric cur- 
rent upon the combinations between metals and metalloids, 
the metals being always deposited on the electro-negative pole, 
and the metalloids on the electro-positive pole. 

However, notwithstanding these properties, differing on the 
one hand and corresponding on the other, a sharp separation 
■of the elements based upon the above-mentioned considera- 
tions cannot be reached, and the classification as regards some 
elements turns out different according to whether one or the 
other behavior is first taken into consideration. 

On the other hand, a classification free from ambiguity re- 
sults from adhering, as is now also done in science, to the be- 
havior of the elements towards salts as the distinctive principle. 
In this manner two sharply-defined groups are obtainable, one 
comprising the elements — the metals — capable of evolving 
hydrogen with the acids, while the elements of the other group 



40 ELECTRO-DEPOSITION OF METALS. 

do not possess this power, and are classed among the metal- 
loids. From this results the following classification : 

Metalloids : Chlorine, bromine, iodine, fluorine, oxygen, 

sulphur, nitrogen, phosphorus, boron, carbon, silicon. 
Metals : Potassium, sodium, lithium, magnesium, calcium,. 

barium, strontium, aluminium, zinc, iron, manganese,. 

chromium, nickel, cobalt, copper, cadmium, arsenic, 

antimony, tin, lead, bismuth, mercury, silver, gold,. 

platinum. 
Acids, bases, salts. Attention has previously been drawn to 
the difference in behavior towards water of combinations of 
the metalloids, and of the metals with oxygen, and this be- 
havior will have to be somewhat more closely considered, 
because we are thereby directed to extremely important classes 
of chemical combinations. 

Oxygen is the most widely distributed element, it forming,, 
together with nitrogen, air, and with hydrogen, water. All 
the elements, with the exception of fluorine and a few more 
rare ones, show great affinity for it and enter readily into re- 
action with it. In the processes enacted thereby, the large 
class of oxides is formed, and the chemical process in which 
an absorption of oxygen takes place is generally called oxida- 
tion, while the term reduction is applied to the opposite process 
by which a withdrawal of oxygen from a substance is effected. 
If these oxides, with the exception of a few so-called indif- 
ferent oxides, be brought together with water, they impart to* 
it either an acid taste, as well as the power to redden blue 
litmus and to evolve hydrogen with metals, or they give to 
the water a lye-like taste and the power of restoring the blue 
color to the litmus previously reddened. The oxides of the 
first kind are chiefly formed with the co-operation of the ele- 
ments belonging to the metalloids, while those of the second 
class contain exclusively metals in addition to oxygen. 

These two classes of bodies, which possess entirely different, 
even directly opposite, properties, are the acids and bases, and 
will have to be separately discussed. 



MAGNETISM AND ELECTRICITY. 41 

Acids. As characteristic properties of the acids have been, 
mentioned, their acid taste, their power of reddening blue 
litmus, and to evolve hydrogen with metals, magnesium being 
especially suitable for the latter purpose. If now the chemical 
compositions of all the compounds which possess the above- 
mentioned properties be more closely examined, they will be 
found to contain, without exception and without regard to 
their own constituents, hydrogen which can be displaced by 
metals. This hydrogen may be present in the combinations 
in one or more atoms, and according to the number of the 
hydrogen-atoms present, a distinction is made between mono- 
basic, dibasic, tribasic, etc., acids. 

A further distinction is made between acids containing no 
oxygen, to which belong the haloid acids for instance, hydro- 
chloric acid, and acids containing oxygen, which are therefore 
called oxy acids. The latter group comprises the majority of 
acids, the well-known sulphuric and nitric acids belonging to 
it. However, the characteristic feature of the acids consists 
solely in that they contain hydrogen which can be displaced 
by metals. 

Bases. The second group of oxides imparts to water, a& 
previously mentioned, a lye-like taste and the power to restore 
the blue color of litmus reddened by acid, and these properties 
are utilized as valuable agents for the characterization of the 
substances as bases. Nevertheless, by the above-mentioned 
definitions the meaning of bases is not unequivocally estab- 
lished, and for a thorough investigation of their material 
nature, their exact composition has to be determined with the 
assistance of analysis, as was done with the acids. From this 
it results that, in addition to metals or metal-like groups of 
atoms, all basic compounds contain oxygen and hydrogen, the 
latter elements being always present in the same number of 
atoms, namely, in the form of hydroxy I groups, OH. Accord- 
ing to their valence the metals combine with one or more 
hydroxyl groups to bases. 

Salts. The groups of chemical combinations above referred' 



42 ELECTRO-DEPOSITION OF METALS. 

1;o, show a very remarkable behavior in so far that by their 
mutual action they are capable of equalizing or saturating 
their characteristic features, so that by means of a basic com- 
bination the specific properties of an acid can be removed, 
and by means of an acid the specific properties of a base. 

An example will explain this process. If to a certain quan- 
tity of hydrochloric acid a "few drops of blue litmus be added, 
the fluid in consequence of its acid properties will change the 
blue coloring matter, the latter acquiring a red color. By 
now adding drop by drop dilute soda lye, which is a basic 
combination, it will be noticed that on the spot where the lye 
falls upon the acid, the red color disappears momentarily, and 
gives way to a blue one. If the addition of lye be carefully 
continued and the fluid constantly stirred, a point is suddenly 
reached when by a single drop of the lye the red color of the 
entire fluid is removed and converted into pale blue. If no 
more lye than exactly necessary for the sudden change in 
color has been brought into the fluid, the latter now possesses 
neither the properties of an acid nor of a base, but has be- 
come what is called neutral. A process of the kind above 
described, by which the acid character of a combination is 
equalized by the basic character of another, or vice versa, is in 
chemistry called neutralization. 

This example shows, that.it is frequently of importance to 
know whether a fluid possesses acid, basic or neutral prop- 
erties, or as it also expressed, whether it shows an acid, basic, 
or neutral reaction. For the determination of these properties 
so-called reagent-papers are used. They consist of unsized 
paper dyed with various organic coloring matters, preferably 
blue litmus tincture, or the latter slightly reddened by acids. 
When small strips of such papers are dipped in the fluid to be 
examined, blue litmus paper will be colored red if the fluid 
has an acid reaction, and red litmus paper, blue, if it shows an 
alkaline or basic reaction. Finally, fluids which change 
neither blue nor red litmus paper react neutral, or they show a 
neutral reaction. If we now return to our example by which 



MAGNETISM AND ELECTRICITY. 43 

the process of neutralization between acid and base has been 
described, it will above all be of interest to learn whether .this 
equalization of the mutual properties runs its course according 
to fixed laws, and what the nature of the latter is. It will be 
further desirable to gain an insight into the chemical trans- 
formations which have taken place in the process, and to learn 
the products which have been newly formed. 

For the elucidation of these questions, let us take a deter- 
mined quantity of. acid and, in the same manner as in the 
above-described example, add to it lye until the acid is just 
neutral, this being shown by the sudden change in color of 
the litmus. If we now take another quantity of the same acid 
-and proceed with it in the same manner, it will be found that 
the consumed quantities of bases stand in the same proportion 
to each other as the quantities of acid used, so that if, in one 
case, for 50 ccm. of acid 30 ccm. of lye were used for neutral- 
ization, in the other, with the use of the same acid and the 
same lye, for 75 ccm. of acid 45 ccm. of lye were required to 
obtain a neutral solution. By repeating these experiments with 
-any other acids and bases, the same conformity to law will 
always be found, and it will thus be seen that neutralization 
between acids and bases runs its course in positively fixed 
quantities, and that for the neutralization of a certain quantity 
of an acid, a positively fixed quantity of a base is required, 
and vice versa. 

Of this conformity to law much use is made in analytical 
chemistry by volumetric methods for the determination of the 
content of an acid by means of a base of known content, and 
vice versa. 

In order to learn what new products are formed by the 
neutralization between acids and bases, the neutral solution 
obtained, according to our example, is concentrated by evapo- 
ration, and it will be found that from the fluid separates a 
white substance in small crystals which, according to analysis, 
consists of sodium (Na) and chlorine (CI), and hence consti- 
tutes the well-known common salt (NaCl). However, in ad- 



44 ELECTRO-DEPOSITION OF METALS. 

dition to the common salt, water (H 2 0) has also been formed 
by the chemical process, as shown by analysis. 

If now, as another example, we take as an acid, sulphuric 
acid" (H 2 S0 4 ), neutralize it with caustic soda (KOH), and 
again determine the products formed, we arrive at a substance, 
the composition of Which, according to analysis, is K 3 S0 4 , 
hence represents potassium sulphate, water being again formed 
as an additional product. The process of neutralization takes 
its course in an analogous manner with any kinds of acids 
and bases, and it will be seen that every neutralization of an 
acid and a base is accompanied by the formation of water, 
and further, that after the withdrawal of the hydrogen from 
the acid, the metal of the bases forms w r ith the remainder a 
new neutral combination, which is called a salt. 

These processes are more distinctly presented by bringing 
them into chemical formulas, and for our examples we have 
to write 

HC1 -f NaOH = H 2 + NaCl. 

Hydrochloric acid. Sodium hydrate. Water. Sodium chloride (common salt). 

H 2 S0 4 + 2KOH = H 2 + K 2 S0 4 . 

Sulphuric acid. Potassium hydrate. Water. Neutral potassium sulphate. 

i 

These formulas show plainly the connection which exists be- 
tween the acids, bases and salts. 

The formation of salts from the acids is thus brought about 
by the replacement of the hydrogen-atoms of the acids by 
metals. However, this replacement of the hydrogen can 
only take place in accordance with the valence of the metal, 
so that a univalent metal can take the place of only one 
hydrogen-atom, a bivalent metal of only two hydrogen-atoms, 
and so on. With the use of a monobasic acid, i. e., one in 
which only one hydrogen-atom is contained in the molecule, 
salts can only be prepared which, besides metal, contain no 
free hydrogen-atoms, and salts of the above-mentioned kind, 
namely, neutral salts, are exclusively obtained. By taking, 



MAGNETISM AND ELECTRICITY. 45 

on the other hand, an acid with several bases, its hydrogen- 
atoms can be either partly or entirely replaced by metals. In 
the first case, salts result which still possess an acid character, 
they containing hydrogen besides a metal, and are called acid 
salts, while in the latter case neutral salts are formed, with 
which we are already acquainted. Sulphuric acid is a dibasic 
acid, and, hence, contains two hydrogen-atoms in the mole- 
cule. Let us take as an example, the salts which sulphuric 
acid is capable of forming, and first saturate in it only one 
hydrogen-atom by a univalent metal, for instance, sodium, 
by adding just enough soda lye to the soda to half saturate it. 
This solution still shows a strong acid reaction, and by suffi- 
ciently concentrating it, a salt is separated which throughout 
possesses acid properties and, as shown by analysis, has the 
chemical formula NaHS0 4 . It is different from the neutral 
sodium sulphate, which is obtained by completely saturating 
the sulphuric acid with caustic soda, i. e., by compounding 
the sulphuric acid with caustic soda up to the neutral reaction. 
The two processes just described are explained by the follow- 
ing equations, which also show distinctly the difference 
between neutral and acid salts : 

-1. H 2 S0 4 + NaOH = NaHS0 4 + H 2 0. 

Sulphuric acid. Sodium Acid sodium Water, 
hydrate. sulphate. 

2. H 2 S0 4 + 2NaOH = Na 2 S0 4 + H 2 0. 

Sulphuric acid Sodium Neutral sodium Water, 

hydrate. sulphate. 

In an analogous manner, as a dibasic acid is capable of 
forming two series of salts, three series of salts may be derived 
from a tribasic acid, for instance, phosphoric acid, so that in 
general an acid of several bases can form as many series of 
acids as it contains hydrogen-atoms in the molecule. 

Nomenclature of salts. In conformity with the definition of 
salts given above, according to which they are derived from 
the acids by the replacement of the hydrogen by metals, they 



46 . ELECTRO-DEPOSITION OF METALS. 

are classified according to the acids they have in common, the 
salts derived from sulphuric acid being thus designated sul- 
phates. For the sake of distinguishing the various metallic 
salts of the same acid, the names of the metals are added. 
Thus, for instance, the scientific term for white vitriol, formed 
by the action of sulphuric acid upon zinc, is zinc sulphate. 
The designations for the salts of the other acids are formed in 
the same manner ; those derived from nitric acid being called 
nitrates, from phosphoric acid, phosphates, etc. Salts in which 
all the hydrogen-atoms of the acids from which they are de- 
rived, have been replaced by metal-atoms are called neutral, 
normal, or primary salts in contradistinction to the acid or 
secondary salts which, besides metal-atoms, also contain 
hydrogen-atoms in the molecule. Finally, the salts are also 
designated by indicating with the assistance of the Greek 
numerals, mono-, di-, etc., the number of metal-atoms con- 
tained in one acid-molecule. With the use of the latter mode 
of designation, the scientific term for the acid sodium sulphate 
is sodium mono-sulphate, and for the neutral sodium sulphate, 
sodium disulphate. 

Fundamental Principles of Electro- Chemistry. 

Electrolytes. Solutions of chemical compounds which can 
be decomposed by the current, are called electrolytes. 

A distinction is made between conductors and non-conductors 
of electricity, and, as previously mentioned, the metals are 
conductors, while most of the metalloids, for instance, sulphur, 
do not transmit the electric current. 

The conductors are divided into conductors of the first class, 
to which belong the metals, and conductors of the second class, 
the latter being chiefly the aqueous solutions of metallic salts 
and certain other substances. 

The conductors of the first class do not experience a per- 
ceptible material change by the passage of the current, they 
being at the utmost heated thereby. On the other hand, the 
conductors of the second class undergo, by the passage of the 



MAGNETISM AND ELECTRICITY. 47. 

current, a chemical change is so far as that on the places 
where the current-carrying metallic conductor enters the 
solution, the constituents of the latter are decomposed and 
separated. 

This phenomenon of the chemical decomposition of sub- 
stances or compounds by means of an electric current is called 
electrolysis, and the conductors of the second class which 
undergo such decomposition, are termed electrolytes. 

The metal plates through which the current passes in and 
out of the solution are called electrodes, the positive electrode 
through which the current enters being termed anode, and 
the negative electrode through which it leaves the electrolyte, 
cathode. 

Ions. This term is applied to the constituents into which 
the combinations present in the solution are decomposed by 
the current, and carried to the cathodes and anodes. 

If a sodium chloride solution be subjected to electrolysis, 
the sodium chloride is decomposed, chlorine being separated 
on the positive electrode, and sodium on the negative electrode. 
Thus chlorine and sodium are the ions of sodium chloride. 
If an acid be decomposed by the electric current, hydrogen is 
always separated on the negative electrode, and the other 
constituent of the acid on the positive electrode. 

The ions separated on the negative electrodes are called 
cations and, hence, in the above-mentioned examples, sodium 
and hydrogen are the cations of sodium chloride, or of the 
acid. The cations migrate from the positive to the negative 
electrode. 

The remaining ions of the combinations migrate from the 
negative to the positive electrode (anode), and are there sep- 
arated. These ions separated on the anode are called anions. 
Thus chlorine is the anion of sodium chloride, as well as of 
hydrochloric acid and of other chlorine compounds. 

The ions exhibit, partly, properties entirely different from 
the elements the names of which they bear. The hydrogen- 
ion of the acids, for instance, is not known as a gas, but only 



48 ELECTRO-DEPOSITION OF METALS. 

in solution, while the element hydrogen is gaseous and but 
very slightly soluble in water. Further, while the hydrogen- 
ion determines the characteristic properties of the acids, hy- 
drogen gas exhibits none of these properties, and the hydrogen- 
ion can only be met with in aqueous solutions of acids in 
which are at the same time, present the other constituents of 
the acids possessing ion-properties. 

; If in hydrochloric acid, hydrogen exists as ion, chlorine 
must be the other ion, because this acid contains no other 
•constituents, and this chlorine-ion possesses the same properties 
exhibited by the chlorine-ions of other combinations in which 
it is contained, hence, in all soluble metallic chlorides. These 
properties of the chlorine-ion, however, differ, entirely from 
those of chlorine in the ordinary elementary state, it possess- 
ing neither its odor nor color ; it exists only in solution and 
has not the bleaching effect of chlorine gas. 

These totally different properties thus clearly indicate that 
the ions have to be considered as modifications of the elements 
designated by the same name, or that the ions have to be 
thought of as existing in a condition different from the elementary 
one ; and the reason for these different conditions and prop- 
erties will be more accurately known after we have to some 
extent become acquainted with the 

Theory of solutions. A solution is not a mere mechanical 
mixture of an invisible, finely divided solid body with the 
solvent, but by solution in a solvent a body partially loses its 
characteristic properties and acquires new ones, and the dis- 
solving process may be viewed as a chemical process in so far 
.as changes of energy (see later on), for instance, fixation or 
disengagement of heat, are connected with it. 

There are not only solutions of solid substances in liquids, 
but also solutions of liquids in liquids, of gases in liquids, and 
of gases in gases. However, the last-mentioned solutions are 
•of interest to us only in so far as it has been shown that the 
laws which they follow are also valid for solutions of solid 
•bodies in liquids. For the proof of this we are indebted to 
•van't Hoff. 



MAGNETISM AND ELECTRICITY. 49 

If a layer of a dilute, pale blue cupric sulphate solution be 
•carefully brought, so as to avoid mixing, upon a concentrated 
cupric sulphate solution of a vivid blue color, and the vessel 
containing the solutions be allowed to stand quietly, it will be 
noticed that the pale blue solution gradually acquires a more 
intense blue color, while the concentrated solution becomes 
paler. The molecules of the cupric sulphate diffuse from the 
stronger, into the weaker solution until the liquid has ac- 
quired a uniform concentration. 

This phenomenon is based upon the same law followed by 
the gases. A gas endeavors, when occasion is offered, to 
•occupy a larger space ;, the energy of motion (kinetic energy) 
inherent in the individual gas molecules propels them until 
their motion is stopped by the walls of the enlarged space. 
The molecules in the cupric sulphate solution possess a similar 
energy of motion and by it, as we have seen, are forced from 
the concentrated, into the weak solution. This force, which 
•corresponds to the gas pressure, is called 

Osmotic pressure. Its presence can readily be demonstrated 
by the following experiment : Fill a glass-cylinder with satur- 
ated sugar solution, close the cylinder air-tight with a semi- 
permeable bladder, and place it upright in a vessel filled with 
water so that the latter stands a few centimeters above the 
bladder ; the bladder bulges up in a short time. This pheno- 
menon is caused by the effort of the sugar molecules to diffuse 
into the surrounding water, being, however, prevented from 
■doing so by the bladder, while water molecules penetrate 
through the bladder into the cylinder. If the cylinder be re- 
moved from the water and the bladder be punctured with a 
pin, the pressure which had existed becomes plainly percepti- 
ble by a jet of fluid being forced upward. By exact investiga- 
tions of the magnitude of osmotic pressure it has been ascer- 
tained that it is proportioned to the number of molecules 
•dissolved in the unit volume, and that the temperature has 
the same effect upon osmotic pressure as upon gases, conformity 
with the laws valid for gases being thus proved. According 
4 



50 ELECTRO-DEPOSITION OF METALS. 

to Avogadro's law equal volumes of different gases under the 
same conditions of temperature and pressure contain equal 
numbers of molecules, and the weights of these gases are thus 
in the same ratio as their respective molecular weights. 

Solutions, as has been proved by van't Hoff, follow the same 
law and, according to van't Hoff, the law applied to them is 
expressed as follows : Solutions which contain an equal num- 
ber of dissolved molecules in the same volume of solvent 
(equimolecular solutions) exert, under the same conditions of 
temperature, the same osmotic pressure which has the same 
value as the gas-pressure these bodies, if in a gaseous state, 
would under the same conditions of temperature exert in a 
volume of gas equal to the volume of solvent. 

It should, however, be borne in mind that the osmotic laws 
are valid only for dilute solutions, just as the gas-law T s hold 
good only for dilute gases. 

Electrolytic dissociation. Clausius originated the idea that 
the molecules of an electrolyte are dissociated to molecular 
particles corresponding to our ions. He supposed that the 
molecules are in constant motion whereby they are partially de- 
composed, and that the molecular particles formed again attract 
the molecular particles of opposite names of the non-decom- 
posed aggregate molecules, and thus effect the dissociation of 
the latter. On the other hand, molecular particles of opposite 
names will again form, under favorable conditions, aggregate 
molecules. However, as soon as a current passes through the 
electrolyte, the irregular and changing movements of the 
molecular particles will cease, and they will take the direc- 
tion presented by the action of the current, i. e., the positive 
molecular particles will wander with the direction of the cur- 
rent to the cathode, and the negative ones to the anode. 

The method, discovered by Raoult, of determining the mole- 
cular weights of dissolved bodies from the elevation of the 
boiling point and the depression of the freezing point, caused, 
in connection with van't Hoff' s osmotic laws, a further investi- 
gation of the dissociation of electrolytes. It was known that 



MAGNETISM AND ELECTRICITY. 51 

salt solutions possess a higher boiling point than the pure 
solvent. Further investigations proved the elevation of the 
boiling point to be proportional to the number of the dissolved 
molecules, and that equimolecular solutions, i. e., solutions 
which contain an equal number of dissolved molecules in the 
same volume of solvent; show the same elevation of the boil- 
ing point. On the other hand, the freezing point of solutions 
is lowered in proportion to the dissolved molecules, and equi- 
molecular solutions show the same depression of the freezing 
point. 

However, not all substances in equimolecular solutions 
furnished at the same temperature, the same osmotic pressure 
as sugar solutions or solutions of other organic bodies. Thus, 
solutions of acids, bases, and salts yielded too high an osmotic 
pressure, and also showed deviations in so far that, as com- 
pared with equimolecular solutions of many organic sub- 
stances, they caused under entirely equal conditions, a higher 
elevation of the boiling point or depression of the freezing 
point. Since, as regards gas-pressure, some gases also do not 
follow Avogadro's law, and these exceptions were explained 
by assuming that the molecules decompose to molecular 
particles, the same assumption was made for solutions of acids, 
bases and salts. 

S. Arrhenius, in 1887, found that all the solutions which 
formed exceptions to the osmotic law and showed deviating 
results as regards elevation of the boiling point and depression 
of the freezing point, possessed the common property of con- 
cluding the electric current, while solutions of organic bodies 
which, as above mentioned, followed the laws referred to, were 
non-conductors of the electric current. Arrhenius ascertained 
that very considerable exceptions appear for water as solvent, 
since the pressure is greater than van't Hoft's law requires, 
and it would therefore be but natural to suppose that sub- 
stances which give too large pressures in aqueous solutions are 
dissociated. He further found that dissociation increases with 
increasing dilution, and he established the law that for every 



52 ELECTRO-DEPOSITION OF METALS. 

dilute solution the ratio of dissociation is equal to the ratio of 
molecular conductivity present to the conductivity of infinite 
dilution, i. e., to the maximum of molecular conductivity. The 
independent particles of the molecules formed are the ions. 

It further follows that it is the ions which take charge of the 
'progressive motion of the current because only ion-forming 
solutions are capable of conducting the current. The ions 
■are supposed to be charged with a certain quantity of -electricity 
— the cations with positive, the anions with negative, electricity 
— and so long as no current passes through the electrolyte, 
they move free in the latter. However, when a current is 
•conducted through the electrolyte, the ions are attracted by 
the electrodes, the positively charged cations by the negatively 
•charged cathode, and the negatively charged anions by the 
positively charged anode. By reason of the movements of the 
ions to the electrodes this phenomenon may be called migration 
of the ions. 

The ions on reaching the electrodes are freed of their charge, 
i. e., they yield their electricity to the electrodes, but they lose 
thereby their ion-nature and are changed into their respective 
elementary atoms ; they show no longer the properties of ions 
but those of the ordinary elements. As is well-known the 
various modifications of carbon (diamond, graphite) are chem- 
ically alike, namely in all cases carbon, but they have entirely 
•different properties, the latter being conditional on an entirely 
different content of energy. 

Energy. By energy is understood the work and everything 
which can be the result from work, and be again converted into 
work. A distinction is made between various kinds of work. 
The effect of mechanical work expresses itself through the pro- 
duct of force and motion, i. e., the force required to convey a 
body a certain distance. If we push a wagon, the force with 
which we push against the wagon multiplied by the motion, 
i. e., the distance the wagon has been pushed, is the value of 
•the work. 

Now a distinction has to be made between the force with 



MAGNETISM AND ELECTRICITY. 53 

which a man in pushing presses against the wagon, and that 
with which the wagon presses against the man, who does the 
pushing. In comparison we speak of both forces as force and 
counter-force, and physics teaches us that force and counter- 
force are, in all cases, of the same magnitude, but exerted in 
opposite directions. Both these propositions may be com- 
bined to the proposition of the conservation of force and work 7 
w r hich reads : No quantity of force and no quantity of ivork are 
lost; the force and ivork consumed are always again met with 
in another definite form. 

When a wagon has been pushed to a higher point of an 
oblique plane, it has taken up a certain quantity of work cor- 
responding to the value from force multiplied by motion in 
the direction of the force. It possesses a certain energy which 
it can and does give up when it is released ; the wagon runs 
down the oblique plane, and the velocity with which it runs 
down is also a form of energy. 

If an article be ground upon an emery wheel, a certain fric- 
tion al work is performed ; the article becomes warm by friction. 
Hence the heat which is developed is another form of energy 
of the frictional work, since according to the law of the con- 
servation of work no quantity of work is lost in nature. 

If carbon (C) be burnt in the air, carbonic oxide (C0 2 ) is 
formed. The law of the conservation of matter teaches us that 
no substance is lost, and hence the quantity of carbonic acid 
which has been formed by combustion must be exactly as 
large as the quantities of carbon and oxygen of the air which 
existed previous to combustion. The carbon and oxygen of 
the air prior to their union to carbonic acid possess a quantity 
of work or energy differing from that after union, the heat 
generated by the combustion being a manifestation of energy 
produced in a chemical way. 

Every element has to be thought of as possessing a definite,, 
inherent content of energy which, when the element enters 
into combination with other elements, may, and generally 
does, undergo a change. Thus in entering into a combination 



54 ELECTRO-DEPOSITION OF METALS. 

the elements yield a portion of their content of energy, gen- 
erally in the form of heat, though sometimes also with lumin- 
ous phenomena, so that the content of energy in the combina- 
tion is less than the content of energy of the elements before 
their union. If now a solution of the combination in water 
be prepared, a change in the content of energy again takes 
place by dissociation, the content of energy present in the 
combination being partially converted into electrical energy. 
The ions appearing thereby receive electrical charges — the 
metal-ions positive charges and the other ions negative charges 
— and the nature of ions may be characterized by saying, they 
differ from the elementary atoms of similar names in having 
a different content of energy. 

Processes on the electrodes. As previously mentioned, in the 
salts all the metal-ions are positive and the other ions of the 
metal combination — the acid residue — negative. 

The ions arriving at the electrodes possess the power of 
entering into chemical processes with the constituents of the 
electrolyte or with the electrodes, as may be shown by the 
following examples : 

When a solution of potassium disulphate (K 2 S0 4 ) is electro- 
lyzed between unassailable platinum, electrodes, the following 
event takes place. The potassium-ions migrate to the cathode 
and separate metallic potassium, 



^-Ko | S0 4 -^ 

Potassium disulphate. 



+ 



which, however, as is well known, cannot exist in water, but 
immediately forms with the solvent potassium hydroxide 
(caustic potash) according to the following equation : 

2K + 2H 2 = 2KOH + H 2 

Potassium Water. Caustic potash. Hydrogen. 

That this transposition takes place in the manner described, 



MAGNETISM AND ELECTRICITY. 55 

is shown by the abundance of hydrogen * which escapes in 
the electrolysis of the potassium disulphate. On the other 
hand, the acid residue S0 4 migrates to the anode, which, as it 
consists of insoluble platinum, cannot saturate the acid residue, 
and the latter is also transposed with water according to the 
following equation : 

S0 4 + H 2 0' = H 2 S0 4 + 

Sulphuric acid residue. Water. Sulphuric acid. Oxygen. 

The oxygen escapes, and the sulphuric acid formed combines 
again to potassium disulphate with the caustic soda formed 
•on the cathode. 

A' like liberation of oxygen takes place when very dilute 
hydrochloric acid f is electrolyzed with platinum anodes. 
Hydrogen escapes on the cathode, but no chlorine appears on 
the anode, an equivalent quantity of oxygen being, however, 
liberated. The water is decomposed by the chlorine, hydrogen 
•chloride and oxygen being formed according to the following 
•equation : 

Cl 2 H- 2H 2 = 4HC1 + 2 

Chlorine. Water. Hydrogen chloride. Oxygen. 

The oxygen appearing in both cases, as well as the hydrogen 
•appearing in the first-mentioned example, are called secondary 
products of electrolysis, because the products first separated 
under the given conditions could not exist and, in being de- 
composed or transposed, formed together with the solvent the 
above-mentioned products. 

When sodium hydroxide (caustic soda) is electrolyzed, 
hydrogen appears on the cathode, because sodium, like potas- 

*This explanation is here retained, though based upon potential measurements, 
it may, according to Le Blanc, be supposed that the hydrogen separates primarily 
and originates from the hydrogen-ions of the dissociated water of the solution. 

f The process does not pass off as smoothly as represented by the formula, but 
the example is given as an illustration according to Ostwald's "Grundlinien der 
Chemie," I. p. 203. 



56 ELECTRO-DEPOSITION OF METALS. 

sium in the former example, cannot exist with water, and 
sodium hydroxide is again formed, hydrogen being at the same 
time liberated. The hydrogen-ion which also cannot exist by 
itself, is discharged on the anode, water and oxygen being 
formed according to the following equation : 

40H = 2H 2 + 2 

Hydroxide. Water. Oxygen. 

Let us now turn to the other cases in which the ions, sepa- 
rated on the electrodes, enter with the latter into chemical 
processes. 

A solution of cupric sulphate (blue vitriol) CuS0 4 is to be 
electrolyzed. The copper ions migrate to the cathode 



<-Cu | S0 4 — > 

Cupric sulphate. 



+ 



and deposit their copper in the form of a galvanic deposit, the 
acid residue — the anion — migrating to the anode. If the 
latter consists of a soluble metal, for instance, copper, the acid 
residue becomes saturated with copper, dissolving approx- 
imately the same quantity of it as has been deposited upon 
the cathode. Theoretically the quantity dissolved from the 
anode by the acid residue should exactly correspond to the 
quantity of metal separated on the cathode. However, in 
practice, such is not the case, because the acid residue is partly 
subject to other decompositions, especially the formation of 
H 2 S0 4 , oxygen being at the same time separated. 

All other processes in which metallic anodes capable of solu- 
tion by the acid residue are used, run their course in a manner 
similar to the electrolysis of blue vitriol. 

As previously mentioned, secondary products may be liber- 
ated by electrolysis. The separation of metal on the cathode 
may also be effected in a secondary manner, and in galvanic 
processes this is mostly brought. about on purpose. Referring 
to the previously mentioned example of the electrolysis of blue 



MAGNETISM AND ELECTRICITY. 57 

vitriol, the copper could only be separated in a primary man- 
ner ; by adding, however, a small quantity of sulphuric acid 
to the blue vitriol solution, separation of copper in a secondary 
manner takes place. The sulphuric acid being in a diluted 
state is more strongly dissociated than the blue vitriol solution, 
the ions of sulphuric acid — hydrogen and acid residue S0 4 — 
first of all taking charge of the conduction of the current, and 
the hydrogen-ions separate the copper on the cathode accord- 
ing to the following equation : 

CuS0 4 + H 2 = Cu + H 2 S0 4 

Cupric sulphate. Hydrogen. Copper. Sulphuric acid. 

In the electrolysis of a silver bath containing potassium- 
silver cyanide (KAgCN 2 ), potassium-ions and silver cyanide- 
ions (AgCN 2 *) appear : 

(a) — | <-K | AgCN 2 -> | + 

From the solution of potassium-silver cyanide the potas- 
sium-ions separate secondarily metallic silver on the cathode, 
potassium cyanide being formed according to the following 
equation : 

(6) K + KAgCN 2 = Ag'+ 2KCN. 

Potassium-ion. Potassium silver cyanide. Silver potassium cyanide. 

The anions AgCN 2 migrate to the anode, are there decom- 
posed to silver cyanide (AgCN) and cyanogen (CN), the 
cyanogen-ions dissolve from the anode silver, silver cyanide 
being formed, and 2 silver cyanide atoms combine with the- 
above (in b) liberated 2 potassium cyanide, to 2 potassium 
silver cyanide atoms : 

(c)Ag + CN = AgCN 

Silver. Cyanogen. Silver cyanide. 

(d) 2AgCN + 2KCN = 2KAgCN 2 

Silver cyanide. Potassium cyanide. Potassium silver cyanide. 

*Hittorf, Ostwald's Klassiker, 23, § 45. 



58 



ELECTRO-DEPOSITION OF METALS. 



The quantities of substances separated from the electrolytes 
by the electric current are subject to fixed laws, which, after 
their discoverer, are named 

Laws of Faraday. These laws are followed by both the 
primary, as well as secondary products of electrolysis, because 
the latter are produced by primary separations, the secondary 
being proportional and chemically equivalent to them. The 
first of these laws is as follows : 

The quantity of substances which is liberated on the electrodes 
is directly proportional to the strength of the electric current which 
has been conducted through the electrolytes, and the time. 

Fig. 7. 




By conducting the current through a closed decomposing 
cell, Fig. 7, filled with acidulated water and furnished with 
two platinum electrodes which are connected with the poles 
•of a source of current, oxygen is evolved on the positive elec- 
trode, and hydrogen on the negative electrode. If the gas- 
mixture (oxyhydrogen gas) which is evolved be caught under 
water in a graduated tube, the. quantity of oxyhydrogen gas 



MAGNETISM AND ELECTRICITY. 



59 



produced by a current of fixed strength within a determined 
time can be readily ascertained. If now a current of double 
the strength be for the same length of time passed through 
the decomposing cell, the quantity of oxyhydrogen gas pro- 
duced will be found twice as large as in the first case. 

Faraday allowed the same quantity of current to pass 
through a series of decomposing cells, coupled one after an- 
other, which contained electrolytes of different compositions, 
and determined quantitatively the separations of cations 
effected in the various cells by an equal quantity of current. 
Suppose the first cell to be a water-decomposing cell like Fig. 
7, let the second cell contain potassium silver cyanide solu- 
tion with a slight excess of potassium cyanide, the third cell 
an acidulated solution of cupric sulphate, and the fourth cell 
a solution of cuprous chloride in hydrochloric acid. 

When electrolysis has been carried on for half an hour, the 
current is interrupted, and the quantity of hydrogen calculated 
from the measured quantity of oxyhydrogen gas produced. 
The platinum cathodes, the weight of which has been deter- 
mined previous to electrolysis, are rinsed in water, next in 
alcohol, and finally in ether. They are then thoroughly dried 
and again weighed to determine the quantities of metal sepa- 
rated in the individual cells. The following quantities were 
found : 



Electrolyte. 



■Quantity of sepa- f 
rated cations. . \ 

For 1 mg. H are 
separated . . . 

Atomic weights. . 



I. 

Dilute 

sulphuric acid 

1:15. 



67 ccm. H = 
6.00 mg. H 

1 mg. H 
1 



II. 

Potassium 

silver cyanide 

KAgC'y 2 . 



650 mg. Ag. 

108.33 mg. Ag. 
108 



III. 

Cupric 
sulphate 
CuS0 4 . 



190 mg. Cu 

31.66 mg. Cu 
63.3 



IV. 

Cuprous 

chloride 

CuCl. 



380 mg. Cu 

63.3 mg. Cu 
63.3 



00 ELECTRO-DEPOSITION OF METALS. 

From this it follows that the separated quantities of cations, 
referred to one part by weight of hydrogen, represent almost 
exactly the quantities of metals which correspond to a single 
valence of their atomic weights. In the electrolytes II and IV, 
the silver atoms and copper atoms are univalent, and in elec- 
trolyte III, bivalent. Hence,' in II and IV were separated the 
quantities of metal, 108.33 mg. silver (error in per cent. 0.33) 
and 63.3 mg. copper, which corresponds to the univalence of 
the atoms, and in III only a valence amounting to 31.56 mg. 
copper which corresponds to the bi valence of the copper atoms 
in cupric sulphate. 

Hence the second law of Faraday, as expressed by v. Helm- 
holtz, reads as follows : The same quantity of current liberates 
in the different electrolytes an equal number of valences or converts 
them into other combinations. 

It has previously been mentioned that for the development 
of 1 g. hydrogen, 96540 coulombs must pass through the 
electrolyte. According to determinations by F. and W. Kohl- 
rausch, 0.3290 mg. copper is liberated from cupric salts by a 
quantity of 1 coulomb, or 31.65 g. by 96540 coulombs. This 
quantity of current is the 

Electro-chemical equivalent, i. e., the number of coulombs 
which split off in one second the portion of atomic weights of 
the cations (metals) or of the anions referred to a valence and 
expressed in grammes, i. e., the gramme-equivalent. Hence, 
for the separation of 1 gramme-equivalent of copper = 31.65, 
or of 1 gramme-equivalent of silver = 108,96540 coulombs are 
always required. 

From the laws of Faraday results the view previously re- 
ferred to, that the passage of the current through the electro- 
lyte is confined to the simultaneous movement of the ions, and 
that no current can pass through the electrolyte if the ions be 
wanting. Hence the ions of the electrolyte are charged or 
combined with specified quantities of electricity, and one por- 
tion of Faraday's law may, according to Ostwald, be thus ex- 
pressed : The quantities of the different ions combined with equal 



MAGNETISM AND ELECTRICITY. 



61 



quantities of electricity are proportional to the combining weights 
of these ions, and the entire law may be summed up as follows : 
In the electrolytes the electricity moves only simultaneously with 
the constituents of the electrolytes which are the ions. The moved 
quantities of electricity are proportional to the quantities of ions, 
and amount to 9654-0 coulombs, or a multiple of them, for one 
molecule of any one ion. 

Below is given a table of the electro-chemical equivalents, 
and from them will be calculated, in the practical part of the 
work, the time required for the formation of deposits of a cer- 
tain specified weight, the current-strength required for the 
purpose, etc. The specific gravities of metals, which are also 
required for the above-mentioned calculations, have been added 
to the table. 



Hydrogen 

Antimony 

Arsenic . 

Cobalt 

Copper from cupric salts . 
Copper from cuprous salts 
Gold from auric salts . . . 
Gold from aurous salts . . 
Iron from ferric salts . . . 
Iron from ferrous salts . . 

Lead 

Nickel 

Platinum .' 

Silver 

Tin from stannic salts . . 
Tin from stannous salts . . 
Zinc 



Electro-chemical 


Deposit in 


Specific 


Equivalent. 


1 Ampei-e-hour 


Gravity. 


0.104 


0.0375 


0.00009 


0.415 


1.4940 


6.8 


0.258 


0.9322 


5.7 


0.305 


1.1001 


8.7 


0.329 


1.1858 


8.8 


0.658 


2.3717 


8.8 


0.681 


2.4513 


19.2 


2.043 


7.3560 


19.2 


0.193 


0.6950 


7.8 


0.289 


1.0423 


7.8 


1.071 


3.8580 


11.3 


0.304 


1.0945 


8.6 


0.504 


1.8160 


21.4 


1.118 


4.0248 


10.5 


0.308 


1.1094 


7.3 


0.616 


2.2180 


7.3 


0.339 


1.2200 


7.2 



Solution-tension of metals. A fluid evaporates on the surface 
until the vapor-pressure produced is equal to the evaporation- 
tension of the fluid. Analogous to this process is the osmotic 
pressure which a salt exercises when dissolved in water, a 
pressure which increases with the quantity of the salt until it 



62 ELECTRO-DEPOSITION OF METALS. 

is in equilibrium with the solution-tension. According to 
Nernst, every metal when immersed in an electrolyte also 
possesses the power conditional to its chemical nature to give 
off metal atoms as ions (cations) to the solution, and this 
power is called solution-tension. 

The solution-tension is the greater the smaller the number 
of cations which are already present in the electrolyte ; if, on 
the other hand, the electrolyte contains a great number of 
cations derived from the dissociation of the salt, the osmotic 
pressure may overbalance the solution-tension, or the osmotic 
pressure may be equal to the solution-tension. 

In the first case, when the solution-tension preponderates, 
the metal will give up to the solution cations charged with 
positive electricity, while an equally large quantity of negative 
electricity remains in the metal. Suppose zinc dipping in 
water, then the zinc-ions passing into solution will be charged 
with positive electricity, while the metal is charged with an 
equally large quantity of negative electricity. 

If the water be replaced by a solution of zinc sulphate 
(white vitriol) which, in consequence of dissociation, already 
contains a larger number of positive zinc-ions and negative 
acid-residue-ions, additional positive zinc-ions will be given 
up to the solution by the zinc so long as the solution-tension 
of the zinc overbalances the osmotic pressure of the dissolved 
zinc-ions. When an equilibrium between osmotic pressure 
and solution-tension is reached, the further formation of zinc- 
ions ceases. 

If the more electro-negative copper be dipped in water it 
also makes an effort to ionize, i. e., to give up to the solution 
copper-ions charged with positive electricity. If, however, the 
water be replaced by cupric sulphate solution, it happens that 
the osmotic pressure of copper-ions formed by dissociation of 
the electrolyte is greater than the solution-tension of the cop- 
per, and hence not only counteracts the formation of new 
copper-ions, but carries positive copper-ions from the electro- 
lyte to the copper, the latter receiving thereby a positive 



MAGNETISM AND ELECTRICITY. 63 

charge, while the fluid surrounding the copper becomes 
negative. 

However, no matter whether the solution-tension may con- 
siderably overbalance the osmotic pressure, by the mere dip- 
ping of the metal in the electrolyte the quantity of ions which 
are newly formed will always be small, because by reason of 
the electrostatic attraction of the cations by the negatively- 
charged metal, there will take place on the contact-surface 
between the metal and the electrolyte an accumulation of 
cations, the osmotic pressure of which will consequently be 
increased, and counteract the solution-tension. The latter 
can only become again active, when the free electricities are 
conducted away by a closed circuit, as will be explained in 
the next section. 

Osmotic theory of the production of the current, according to 
Nernst. The behavior of zinc in a zinc sulphate solution, and 
that of copper in a cupric sulphate solution, has above been 
referred to. If a cell be put together of zinc dipping in zinc 
sulphate solution, and copper in cupric sulphate solution, such 
as a Daniell cell, in which the two solutions are separated by 
a porous partition, called a diaphragm, the following processes 
take place : 

From the zinc, positive zinc-ions pass into solution so long 
as the, at first, slighter osmotic pressure of the electrolyte 
balances the solution-tension ; the zinc becomes negatively 
electric and the electrolyte positively electric on the contact- 
surface. By the preponderance of the osmotic pressure of the 
copper sulphate solution over the solution-tension of the 
copper, positive copper-ions are separated on the copper, and 
yield their positive charges to the latter. They themselves are 
transformed from the ion state into the molecular state, thus 
becoming non-electric, while on the contact-surface the cupric 
sulphate solution becomes negatively electric. Hence a state 
of rest supervenes, in which the zinc is charged with negative, 
and the copper with positive, electricity, while the zinc solution 
is charged positively and the copper solution negatively. If 



'64 ELECTRO-DEPOSITION OF METALS. 

now by means of a metallic wire the zinc be outside of the 
solutions connected with the copper, thus, establishing a closed 
circuit, the following process takes place : The positive elec- 
tricity in the copper migrates through the wire to the zinc, 
and neutralizes the quantity of negative electricity present in 
the latter. By the flow of positive electricity from the copper 
the state of equilibrium, which existed between copper and 
■cupric sulphate, is disturbed, and the osmotic power being now 
predominant, the solution again gives up cojDper-ions to the 
copper, whereby the latter is again charged with positive 
•electricity. On the other hand, after the exchange of elec- 
tricities in the zinc by the solution-tension, fresh zinc-ions can 
be brought into solution. Thus a current flows continuously 
from copper to zinc until either no more copper-ions are 
-conveyed from the cupric sulphate solution to the copper, or 
until all the zinc is ionized, i. e., dissolved. 

Nernst's conception of the solution-tension of the metals is 
analogous to that of the osmotic pressure, the impelling force 
•of a Daniell battery having the character of a pressure, and 
for that reason Ostwald designates a galvanic battery as a 
machine driven by osmotic pressure, eventually by electrolytic 
solu tion-tension . 

The electro-motive force of such a cell is mainly determined 
by the magnitude of the solution-tension of the metals. In 
the closed cell the metal gives up with greater solution-tension 
its atoms as ions into the electrolyte in which it is confined, 
while the cations of the other electrolyte are discharged 
on the metal contiguous to it and pass into the molecule state. 
By this, the dissolving metal, to which the anions of the other 
electrolyte — the acid residue — migrate, becomes the anode, and 
the other metal on which the cations of its electrolyte separate 
non-electrically, the cathode. Since the cations are discharged 
on the cathode, the latter is also called the conducting elec- 
trode, and the anode which dissolves, the dissolving electrode. 

From what has been said, it might appear that the current 
in a Daniell cell owes its existence to purely physical forces. 



MAGNETISM AND ELECTRICITY. 65 

The solution-tension of the metals depends, however, on their 
chemical affinity, and the current is actually electric energy 
which has been formed from chemical energy. The solution 
of the anode-metal is a chemical process, whereby the cations 
are forced from the electrolyte surrounding the anode ; the 
anode-metal endeavors to expand, and hence the mode of 
action of chemical affinity in converting chemical into electric 
energy may be designated as the effect of pressure. 

However, additional chemical processes take place in the 
Daniell cell ; the zinc dissolves to zinc sulphate because the 
anions of the cupric sulphate solution migrate to the zinc, 
while from this solution a quantity of copper equivalent to 
the dissolved zinc is deposited on the cathode. By the anion 
SO 4 of the cupric sulphate solution an oxidation of the zinc 
takes place, the latter acting therefore as a reducing agent. 
The cupric sulphate solution, on the other hand, is reduced to 
copper, and the acid-residue S0 4 being liberated thereby acts 
as an oxidizing agent, while the copper of the cathode remains 
chemically unchanged. Since, according to Ostwald, in every 
chemical process which takes place between an oxidizing and 
a reducing agent, variations appear in the ion-charges by 
reason of the varying capacities of the ions to absorb or dis- 
charge more quantities of electricity, such cells are also called 
oxidizing and reducing cells. Concentration cells will later on 
be referred to. 

Polarization. By polarization is understood the appearance 
of a counter-current passing in a direction opposite to that of 
the current conducted into an electrolyte ; the main current is 
therefore weakened by this counter-current. Polarization 
takes place when the current produces substantial changes in 
the electrolytes or on the electrodes, no matter whether such 
changes consist in a difference of the nascent concentrations of 
the' electrolyte, or in the formation of gas-cells by the separa- 
tion of layers of gas on the electrodes, etc. 

If a weak current be conducted into a cell filled with stand- 
ard cupric sulphate solution, both electrodes of which consist 
5 



66 ELECTRO-DEPOSITION OF METALS. 

of copper, and a galvanometer be placed in the circuit, it will! 
be noticed that an electrolytic decomposition takes place. The 
copper-ions discharged from the copper solution on the elec- 
trode connected with the negative pole of the source of current, 
pass into the molecular state, and metallic copper separates 
upon this electrode, while the anions of the acid-residue SO 4. 
migrate to the electrode connected with the positive pole, 
where they dissolve copper, thus giving up fresh copper-ions- 
to the solution. Hence the concentration of the electrolyte 
remains constant, provided electrolysis lasts not too long, and 
the current introduced is not stronger than just necessary for 
the decomposition of the cupric sulphate solution ; the nature 
of the electrodes themselves remains unchanged. The needle 
of the galvanometer makes one deflection and when the cur- 
rent is interrupted returns to the point, thus indicating the 
absence of a counter-current ; the electrodes have proved them- 
selves as non-polarizable. 

However, the case is different when an electrolyte is electro- 
lyzed between insoluble electrodes. If a powerful current be 
conducted through a platinum anode into standard snlphurie 
acid (H 2 S0 4 ), the latter is decomposed into hydrogen-ions 
which go to the platinum cathode while the S0 4 -ions migrate 
to the anode. As previously mentioned, the S0 4 -ions cannot 
exist in a free state, neither can they dissolve platinum and, 
while water is decomposed, sulphuric acid and oxygen-gas are 
again formed, the latter being separated on the platinum 
anode. The hydrogen separated on the cathode is electro- 
positive towards the oxygen separated on the anode, the con- 
sequence being that from the hydrogen of the cathode a 
counter-current flows to the oxygen of the anode, which is in- 
dicated when the primary current is interrupted by the needle 
of the galvanometer, instead of merely returning to the O 
point, deflecting in a direction opposite to that of the previous 
deflection, and returning to the point only after the equal- 
ization of the charges in the electrodes. 

The counter-current or polarization-current appears also 



MAGNETISM AND ELECTRICITY. 67 

when two different metals dip in one electrolyte. In a Volta 
cup cell, a zinc plate and a copper plate connected by a metal- 
lic wire dip in dilute sulphuric acid. A current flows from 
the copper through the wire to the zinc, and returns from the 
zinc through the acid to the copper, decomposing thereby the 
acid into hydrogen and S0 4 . The hydrogen separates on the 
copper, the acid-residue S0 4 on the zinc, and dissolves the 
latter, zinc sulphate being formed. The separated hydrogen 
being electro-positive towards the separated acid-residue, a 
current in the direction from the copper to the zinc is gener- 
ated, and consequently flows in a direction opposite to that of 
the main current, which passes from the zinc to the copper. 
The electro-motive force of the main current is thus decreased 
by the magnitude corresponding to the electro-motive force of 
this counter-current. 

If a zinc chloride solution be electrolyzed between two plat- 
inum electrodes, zinc separates on the cathode while chlorine 
appears on the anode. If the current be interrupted, a galvano- 
scope placed on the electrodes indicates a vigorous counter- 
current which turns from the zinc deposit — hence the cathode 
— to the anode, therefore opposite to the current at first sup- 
plied. This counter-current originates from the tendency of 
the substances separated on the electrodes to return, in conse- 
quence of the solution-tension, to the ion state, and this ten- 
dency exists during the entire process of the electrolysis. 

The farther the metals in the series of electro-motive force 
are distant from each other, the greater the electro-motive 
force which the polarization-current possesses, as will be more 
particularly shown in the "practical part of this work. 

Decomposition-pressure. An electric current can only pass 
through an electrolyte and decompose it, when its electro- 
motive force possesses a certain minimum magnitude. The 
characteristic values at which the electrolytes are permanently 
decomposed are designated, according to Le Blanc, as their 
decomposition-values; the decomposition-pressure being the 
electro-motive force required for the separation of the electric 



68 ELECTRO-DEPOSITION OF METALS. 

charge of the ions. The decomposition-values of solutions 
which separate metals vary. Le Blanc found as decomposi- 
tion-values of solutions which contained per liter one combin- 
ing weight of the metallic salts, for 

Zinc sulphate, 2.35 volt ; Cadmium sulphate, 2.03 volt. 

Nickel sulphate, 2.09 volt ; Cadmium chloride, 1.88 volt. 

Nickel chloride, 1.85 volt ; Cobaltous sulphate, 1.92 volt. 

Silver nitrate, 0.70 volt; Cobaltous chloride, 1.78 volt. 

The difference in the decomposition values of metallic salt 
solutions explains the feasibility of separating from a solution 
which contains different metals, the individual metals, one 
after the other, free from other admixtures. 

Velocity of ions. It has previously been shown that no 
polarization-current is generated when a cupric sulphate solu- 
tion is for a short time electrolyzed between copper-electrodes. 
If, however, not too strong a current be for a longer time 
passed through the solution, a polarization-current appears, 
the origin of which must be due to another cause than the 
formation of a gas cell, because no gases are separated with 
not too strong a current. It has been shown that changes of 
concentration take place in the solution, concentration becom- 
ing greater on the cathode and less on the anode. These 
changes in concentration have been subjected to a thorough 
investigation by Hittorf, and it was found that the former 
view, according to which the number of positive and negative 
ions which migrate in opposite directions through an elec- 
trolyte, must be equal, was an erroneous one. The mobility 
of the ions varies, and depends on their nature. If, for in- 
stance, hydrochloric acid be electrolyzed, the hydrogen-ion 
migrates about five times as rapidly to the cathode as the 
chlorine-ion to the anode. The cations and anions of the 
metallic salts act in a similar manner, and consequently a 
greater concentration will take place on the cathode and a re- 
duction in the content of metal on the anode, when the anions 
migrate more slowly than the cations ; and vice versa, concen- 
tration will increase on the anode when the anions migrate 
more rapidly than the cations. 



MAGNETISM AND ELECTRICITY. 69 

The middle layer of the electrolyte always remains un- 
changed and of the same concentration, the changes in con- 
centration being shown in the layers of fluid surrounding the 
electrodes, and these differences in concentration also effect 
the formation of a current, which, according to the nature of 
the electrodes may flow in the sense of the main current or in 
that of the counter-current. 

The quotients obtained by dividing the distances, which the 
cations and anions perform in the same time, by the total dis- 
tance of the road traveled by the two ions, Hittorf designates 
as the transport-values of the respective ions. 

We herewith conclude the theoretical considerations, and 
w T ill later on have occasion to touch upon other fundamental 
electrolytical principles of less importance. 



III. 

SOURCES OF CURRENT. 



CHAPTER III. 



VOLTAIC CELLS, THERMO-PILES, DYNAMO-ELECTRIC MACHINES, 

ACCUMULATORS. 

The sources of current which are used for the electro- 
deposition of metals are : Voltaic cells, thermo-piles, dynamo- 
electric machines, and accumulators. 

A. Voltaic Cells. 

It is not within the province of this work to enter into a 
detailed description of all the forms of voltaic cells, because 
the number of such constructions is very large, and the num- 
ber of those which have been successfully and permanently 
introduced for practical work is comparatively small. 

In the theoretical part, we have learned the origin of the 
current and the explanation of its origin by the solution- 
tension of the metals or the osmotic pressure of the solutions, 
and we know further that in a voltaic cell chemical energy is 
converted into electrical energy. In speaking of polarization 
which is formed when two different metals dip in one fluid, 
we have seen that the hydrogen liberated on the copper in 
a Volta cup cell generates a counter-current which weakens 
the principal current. This hydrogen appearing on the posi- 
tive pole is the cause of a rapid decrease in the efficiency of 
the cell, and all cells in which the hydrogen on the cathode 
is not neutralized by suitable means, are called inconstant cells, 
while cells in which the hydrogen is removed in a physical 

(70) 



SOURCES OF CURRENT. 71 

way or by chemical agents which oxidize it, are called constant 
cells. 

The original form of voltaic cells, the voltaic pile, consisting 
of zinc and copper plates separated from one another by moist 
pieces of cloth, has already been mentioned on p. 2, as well as 
its disadvantages, which led to the construction of the so-called 
trough battery. The separate elements of this battery are 
square plates of copper and zinc, soldered together, and 
parallel fixed into water-tight grooves in the sides of a wooden 
trough so as to constitute water-tight partitions, which are 
filled with acidulated water^ The layer of water serves here 
as a substitute for the moist pieces of cloth in the voltaic pile. 

In other constructions the fluid is in different vessels, each 
vessel containing a zinc and a copper plate which do not 
touch one another, the copper plate of the one vessel being 
•connected with the zinc plate of the next, and so on. 

In all cells with one exciting fluid, the current is quite 
strong at first, but decreases rapidly for the reasons given above. 
On the one hand, during the interruption of the current a 
change takes place in the fluid by the local effect in the cell, 
and, on the other, the zinc forms with the impurities contained 
in it, small voltaic piles with a closed circuit, in consequence 
of which the cell performs a certain chemical work even when 
the current is interrupted. The local action can be reduced 
to a minimum by amalgamating the zinc. Such amalgama- 
tion is also a protection against the above-mentioned chemical 
work of the cell, the hydrogen bubbles adhering so firmly 
during the interruption of the current to the amalgamated 
homogeneous surface as to form a layer of gas around the zinc 
surface by which its contact with the fluid is prevented. 

Amalgamation may be effected in various ways. The zinc is 
either scoured with coarse sand moistened with dilute sulphuric 
or hydrochloric acid, or pickled in a vessel containing either of 
the dilute acids. The mercury may be either mixed with moist 
sand and a few drops of dilute sulphuric acid, and the zinc be 
amalgamated by applying the mixture by means of a wisp of 



72 ELECTRO-DEPOSITION OF METALS. 

straw or a piece of cloth ; or the mercury may be applied by 
itself by means of a steel-wire brush, the brush being dipped in 
the mercury and what adheres is quickly distributed upon the 
zinc by brushing until the entire surface acquires a mirror-like 
appearance. The most convenient mode of amalgamation is 
to dip the zinc in a suitable solution of mercury salt and rub 
with a woolen rag. A suitable solution is prepared by dissolv- 
ing 10 parts by weight of mercurous nitrate in 100 parts of 
warm water, to which pure nitric acid is added until the milky 
turbidity disappears. Another solution, which is also highly 
recommended, is obtained by dissolving 10 parts by weight of 
mercuric chloride (corrosive sublimate) in 12 parts of hydro- 
chloric acid and 100 of water, or by dissolving 10 parts by 
weight of potassium mercuric cyanide and 2 parts potassium 
cyanide in 100 parts of water. In order to preserve as much 
as possible the coating of mercury upon the zinc, sulphuric 
acid saturated with neutral mercuric sulphate is used for the 
cells. For this purpose frequently shake the concentrated 
sulphuric acid (before diluting with water) with the mercury 
salt. As much mercuric sulphate or mercuric chloride as will 
lie upon the point of a knife may also be added in the cells to 
the zinc. 

Instead of the addition of mercuric sulphate, Bouant recom- 
mends to compound the dilute sulphuric acid with 2 per cent, 
of a solution obtained as follows : Boil a solution of 3^ ozs. of 
nitrate of mercury in 1 quart of water, together with an excess 
of a mixture of equal parts of mercuric sulphate and mercuric 
chloride, and, after cooling, filter and use the clear solution. 

Smee cell. This cell consists of a zinc plate and a platinized 
silver plate dipping into dilute acid. It may be formed of two 
zinc plates mounted with the platinized silver between them 
in a wooden frame, which being, a very feeble conductor may 
carry away a minute fraction of the current, but serves to hold 
the metals in position, so that quite a thin sheet of silver may 
be employed without fear of its bending out of shape and 
making a short circuit. Platinizing is effected by suspending 



SOURCES OF CURRENT. 



73 



the silver plates in a vessel filled with acidulated water, add- 
ing some chloride of platinum and placing the vessel in a 
porous clay cell filled with acidulated water and containing a 
piece of zinc, the latter being connected with the silver plates 
by copper wire. The platinum coating obtained in this man- 
ner is a black powder which roughens the surfaces, in conse- 
quence of which the bubbles of hydrogen become readily de- 
tached, and polarization is less than with silver plates not 
platinized. The use of electrolytically-prepared copper plates, 
which are first strongly silvered and then platinized, is still 
more advantageous on account of their greater roughness. 
To increase the constancy of the cell, it is advisable to add: 
some chloride of platinum to the dilute acid of the element. 

The Smee cell is still frequently used in England and the 
United States with silver and gold plating solutions. Its 
electro-motive force is about 0.48 volt. 

As previously mentioned, polarization can be entirely 
avoided only by allowing the electro-negative pole-plate to 
dip in a fluid which, by combustion, reduces the hydrogen 
evolved to water, or, in other words, which immediately oxi- 
dizes the hydrogen to water. From this 
conviction originated the so-called constant 
cells with two fluids, the first of these cells 
being, in 1829, constructed by Becquerel, 
which, in 1836, was succeeded by the more 
effective one of Daniell. 

Daniell cell. In its most usual form 
Daniell 's cell (Fig. 8) consists of a glass 
vessel, a copper cylinder, a porous earthen- 
ware pot and a zinc rod suspended in the 
latter. The glass vessel is filled with 
saturated blue vitriol solution, a small piece of blue vitriol 
being added, and the porous earthenware pot with dilute 
sulphuric acid about 1 part of acid to 12 to 20 parts of water. 
The acid residue S0 4 migrates to the positive zinc, and there 
forms zinc sulphate, while the hydrogen which is liberated on 



Fig. 8. 




74 



ELECTRO-DEPOSITION OF METALS. 



Meidinger cell. 



Fig. 9. 



the electro-negative copper, reduces from the blue vitriol 
solution an equivalent quantity of copper, which is deposited 
upon the electro-negative plate according to the following 
equation : 

CuS0 4 + 2H = Cu + H 2 S0 4 

Cupric sulphate. Hydrogen. Copper. Sulphuric acid. 

Thus the hydrogen is removed by its combining with the 
acid-residue S0 4 to sulphuric acid. A drawback of the 
Daniell cell is that the blue vitriol solution diffuses into the 
porous pot, where it is decomposed by the zinc on coming in 
contact with it, and the copper is separated upon the zinc, the 
efficiency being thus destroyed, or at least very much weak- 
ened. The electro-motive force of the Daniell cell is quite 
exactly 1.1 volt. 

This may be considered a modified Daniell 
cell. Like the Callaud cell, it has no 
porous partition, the mixture of the two 
fluids being retarded by their different 
specific gravities. The form of the Meid- 
inger cell, as most generally used, is 
shown in Fig. 9. 

* Upon the bottom of a glass vessel, A, 
provided at b with a shoulder, stands a 
small glass cylinder, K, which contains 
the electro-negative copper cylinder D; 
from the latter a conducting wire leads to 
the exterior. Upon the shoulder, at 6, 
rests the zinc cylinder Z, which is also 
provided with a conducting wire leading 
to the exterior. The balloon C closes the 
vessel by being placed upon it. The balloon is filled with pieces 
of blue vitriol and Epsom salt solution. The entire cell is also 
filled with Epsom salt solution (1 part Epsom salt to 5 water.) 
In the balloon C concentrated solution of blue vitriol is formed 
which flows into the glass cylinder K. If the battery is not 




SOURCES OF CURRENT. 75 

closed, the concentrated copper solution remains quietly stand- 
ing in K, its greater specific gravity preventing it from rising 
higher and reaching the zinc. If, however, the current be 
closed, zinc is dissolved, while metallic copper is separated 
from the blue vitriol solution, and concentrated solution flows 
from the balloon G to the same extent as the blue vitriol solu- 
tion in D becomes dilute by the separation of copper. Hence 
the action of the cell remains constant for quite a long time, 
and of all the modified forms of Daniell's cell consumes the 
least blue vitriol for a determined quantity of current. How- 
ever, in consequence of its great internal resistance (3 to 5 
ohms, according to its size) its current-strength is small. The 
electro-motive force of the Meidinger cell is 0.95 volt. 

Bunsen cell. Bunsen, in 1841, replaced the expensive plati- 
num by prisms cut from gas-carbon, which is still less electro- 
negative than platinum, and very hard and solid, so that it 
perfectly resists the action of the nitric acid. In place of the 
gas-carbon an artificial carbon may be prepared by kneading 
a mixture of pulverized coal and coke with sugar solution or 
syrup, bringing the mass under pressure into suitable iron 
moulds and heating it red-hot, the air being excluded. After 
cooling the carbon is again saturated with sugar solution 
(others use tar, or a mixture of tar and glycerine) and again 
heated, the air being excluded. These operations are, if 
necessary, repeated once more, especially when great demands 
are made on the electro-motive force and solidity of the 
artificial carbons. 

In the Bunsen cell the zinc electrode dips in dilute sulphuric 
acid and the carbon in concentrated nitric acid. Independent 
of the fact that by reason of its rough surface, the carbon has 
by itself the tendency to repel the hydrogen-bubbles and thus 
acts to a certain degree as a depolarizer, depolarization, i. e.,. 
the removal of the hydrogen-bubbles which produce polariza- 
tion, is most effectively assisted by the nitric acid, the hy- 
drogen being oxidized to water according to the following 
equation, while the nitric acid is reduced to nitric oxide: 



76 



ELECTRO-DEPOSITION OF METALS. 



2HN0 8 

Nitric acid. 



+ 6H 

Hydrogen. 



2NO 

Nitric oxide. 



4H 2 

Water. 



The processes which take place in the Bunsen cell are as 
follows : From the positive carbon a current passes through 
the wire to the zinc and returns from the latter through the 
dilute sulphuric acid to the carbon. The sulphuric acid 
(H 2 S0 4 ), is thereby decomposed to hydrogen and sulphuric 
acid residue S0 4 the hydrogen migrating to the carbon and is 
oxidized to water by the nitric acid, while the sulphuric acid 
residue migrates to the zinc and combines with it to zinc sul- 
phate (ZnS0 4 ) as illustrated by the following scheme : 




Sulphuric acid | Nitric acid 



H 2 S0 4 



2HNO, 



Carbon 

( + )C 




\< / ■ \ / 




\ 



ZnS0 4 (Zinc sulphate) 2HN0 3 (Nitric acid) H 2 (Hydrogen) 



\ 



At 



/ 



K,0, 

Nitrogen tetroxide 



+2H 2 
Water. 



To prevent the two fluids from mixing, the use of a porous 
partition is required, the same as in DanielFs cell. 

Figs. 10, 11 and 12 show three forms of Bunsen's cell gen- 
erally used. 

Fig. 11 is the most convenient and practical form. It con- 
sists of an outer vessel of glass or earthenware. In this is 
placed a cylinder of zinc in which stands a porous clay cup, 
and in the latter the prism of gas-carbon. This substance is 
the graphite of the gas retorts. It is not coke. It is easily 
procurable in lump at a small price, but costs much more when 
cut into plates, as, when the material is good, it is exceedingly 



SOURCES OF CURRENT. 



77 



difficult to work. It is generally cut with a thin strip of iron 
and watered silver-sand. Blocks for Bunsen cells cost less be- 
cause they are more easily produced. Rods for Bunsen cells 
should be a few inches longer than the pots to protect the top 
from contact with the acid. A good carbon is of a clear gray 
appearance, has a finely granulated surface, and is very hard. 
A band of copper is soldered or secured by means of a bind- 
ing-screw to the zinc cylinder, while the prism of gas carbon 
carries the binding-screw (armature), as seen in Fig. 10 in the 
upper part of which a copper sheet or wire is fixed for the 
transmission of the current. The other vessel is filled with 



Fig. 10. 



Fig. 11. 



Fig. 12. 






dilute sulphuric acid (1 part by weight of sulphuric acid of 
66° Be. — free from arsenic — and 15 parts by weight of water), 
and the porous cup with concentrated nitric acid of at least 
36° Be., or still better 40° Be., care being had that both 
fluids have the same level. 

In Fig. 11 the cylinder of artificial carbon is in the glass 
vessel, while the zinc, which, in order to increase its surface, 
has a star-shaped cross-section, is placed in the porous clay 
cup. In this case the outer vessel is filled with concentrated 
nitric acid, and the clay cell with dilute sulphuric acid. 

The form of the Bunsen cell shown in Fig. 10 is more 
advantageous, because its effective zinc surface can be kept 
larger. 



78 



ELECTRO-DEPOSITION OF METALS. 



Fig. 12 shows a plate cell such as is chiefly used for plunge 
batteries. 

Fig. 13 shows an improved Bunsen cell of great power. It 
is particularly adapted for use with nickel, copper, brass or 
bronze solutions. It has an electro-motive force of 1.9 volts. 
Where the absence of power prevents the use of a dynamo, a 
battery of these cells is very suitable for nickel plating. 

The Bunsen cells are much used for electro-deposition, since 
they possess a high electro-motive force (1.88 volts), and, on 
account of slight resistance (0.5 to 0.25 ohm, according to 

Fig. 13. 




their size), develop considerable current-strength. Like the 
Grove cells, they have the inconvenience of evolving vapors of 
nitrogen tetroxide, which are not only injurious to health, but 
also attack the metallic articles in the workshop. Wherever 
possible they should be placed in a box at such a height that 
they may be readily manipulated. The box should have 
means of ventilation in such a way that the air coming in at 
the lower part will escape at the top through a flue, and carry 
away with it the acid fumes disengaged. It is still better to 
keep the cells in a room separate from that where the baths 
and metals are located. Furthermore, as the nitric acid be- 



SOURCES OF CURRENT. 79' 

comes diluted by the oxidation of the hydrogen, and the sul- 
phuric acid is consumed in the formation of sulphate of zinc, 
the acids have to be frequently renewed. 

To get rid of the acid vapors, as well as to render the cells 
more constant, A. Dupre has proposed the use of a 30 per 
cent, solution of bisulphate of potash in water, in place of the 
dilute sulphuric acid, and a mixture of water 600 parts, con- 
centrated sulphuric acid 400, sodium nitrate 500, and bichro- 
mate of potash 60, in place of the nitric acid. 

The following method can be recommended : The outer 
vessel which contains the zinc cylinder is filled with a mode- 
rately concentrated (about 30 per cent.) solution of bisulphate 
of potash or soda, and the clay cup with solution of chromic 
acid — 1 part chromic acid to 5 parts water. As soon as the 
electro-motive force of the cell abates, it is strengthened by 
the addition of a few spoonfuls of pulverized chromic acid to 
the chromic acid solution. It is preferable to use the chromic 
acid in the form of a powder especially prepared for this pur- 
pose than a chromic acid solution produced by mixing potas- 
sium dichromate solution with sulphuric acid, such a solution 
having a great tendency to form crystals which exerts a dis- 
turbing effect. Solution of sodium dichromate compounded 
with sulphuric acid does not show this drawback. 

The efficiency of the chromic acid solution rapidly abates in 
a comparatively short time, the electro-motive force of the cell 
decreasing in a few hours and chromic acid has frequently to 
be added, or the cell eventually refilled. 

Dr. Langbein has succeeded in preparing a soluble chrom- 
ium combination which depolarizes rapidly and for a longer 
time maintains the efficiency of the cell constant. With a 
single filling of this solution, the battery has been kept work- 
ing for six days, from morning to evening, without refilling 
being required. During the night the batter}^ remained 
filled, but inactive. The solution is obtained by treating 
Langbein's chromic iron powder with concentrated sulphuric 
acid and carefully diluting with water. 



80 ELECTRO-DEPOSITION OF METALS. 

The electro-motive force of a cell filled with this solution is 
1.8 volts. Considering the lasting quality and great con- 
stancy, and consequent cheapness, as well as freedom from 
odor of this solution, it would appear to be the most suitable. 

If nitric acid is used for filling the cells it is advisable in 
order to decrease the vapors, to cover the acid with a layer of 
oil £ to | inch deep. 

The binding-screws which effect the metallic contacts must 
■of course be frequently inspected and cleaned, the latter being 
best done by means of a file or emery paper. It is advisable 
to place a piece of platinum sheet between the binding surface 
of the carbon armature and the carbon, in order to prevent 
the acid, rising through the capillarity of the carbon, from 
acting directly upon the armature (generally brass or copper). 
To prevent the acid from rising, the upper portions of the 
carbons may be impregnated with paraffine. For this pur- 
pose the carbons are placed £ to 1 inch deep in melted paraffine 
and allowed to remain 10 minutes. On the sides where the 
armature comes in contact with the carbon, an excess of par- 
affine is removed by scraping with a knife-blade or rasp. 

Treatment of Bunsen cells. Before use the zincs should be 
carefully amalgamated according to one of the methods given 
on page 71. The nitric acid need not be pure, the crude com- 
mercial article answering very well, but it should be as concen- 
trated as possible and show at least 30° Be. Carbons of hard 
retort-carbon are to be preferred, although those cut from 
carbon produced in gas-houses, gasifying coal without an 
addition of lignite, may also be used. Artificial carbon, if 
-employed, should be examined as to its suitability, the non- 
success of the plating process being frequently attributed to the 
composition of the bath, when in fact it is due to the defective 
carbons of the cells. In order to avoid an unnecessary con- 
sumption of zinc and acid, the cells are taken apart when not 
in use, for instance, over night. Detach the brass armature 
of the carbon and lay it in water to which some chalk has 
been added. Lift the carbon from the clay cylinder and place 



SOURCES OF CURRENT. 81 

it in a porcelain dish or earthenware pot ; empty the nitric acid 
of the clay cup into a bottle provided with a glass stopper ; 
place the clay cup in a vessel of water, and finally take the 
zinc from the dilute sulphuric acid and place it upon two 
sticks of wood laid across the glass vessel to drain off. In put- 
ting the cells together the reverse order is followed, the zinc 
being first placed in the glass vessel and then the carbon in the 
porous clay cup. The latter is then filled about three-quarters 
full with used nitric acid, and fresh acid is added until the fluid 
in the clay cup stands at a level with that in the outer vessel. 
The cleansed brass armature is then screwed upon the carbon. 
Finally, add to the dilute sulphuric acid in the outer vessel a 
small quantity of concentrated sulphuric acid saturated with 
mercury salt. 

It is advisable to have at least a duplicate set of porous clay 
cups, and, in putting the cells together, to use only cups which 
have been thoroughly soaked in water. The reason for this 
is as follows: The nitric acid fills the pores of the cup, and, 
finally reaching the zinc of the outer vessel, causes strong local 
action and a correspondingly rapid destruction of the zinc. It 
is, therefore, best to change the clay cups every day, allowing 
those which have been in use to lie in water the next day with 
frequent renewal of the water. . For the same reason the nitric 
acid in the clay cup should not be at a higher level than the 
sulphuric acid in the outer vessel. 

When the Bunsen cells are in steady use from morning till 
night, the acids will have to be entirely renewed every third 
or fourth day. The solution of sulphate of zinc in the outer 
vessel, being of no value, is thrown away, while the acid of the 
clay cells may be mixed with an equal volume of concentrated 
sulphuric acid, and this mixture can be used as a preliminary 
pickle for brass and other copper alloys. 

The Leclanche cell (zinc and carbon in sal-ammoniac solu- 
tion with manganese peroxide as a depolarizer) need not be 
further described, it not being adapted for regular use in electro- 
plating. It is in very general use for electric bells, its great 
6 



82 



ELECTRO-DEPOSITION OF METALS. 



recommendation being that, when once charged, it retains its 
power without attention for a long- time. 

Cupric oxide cell. Lallande and Chaperon have introduced 
a cupric oxide cell shown in Fig. 14 which possesses certain 
advantages. It consists of the outer vessel G, of cast-iron or 
copper, which forms the negative pole-surface, and to which 
the wire leading to the anodes is attached, and a strip of zinc, 
Z, coiled in the form of a spiral, which is suspended from an 

Fig. 14. 




ebonite cover carrying a terminal connected with the zine. 
The hermetical closing of the vessel G by the ebonite cover is 
effected by means of three screws and an intermediate rubber 
plate. Upon the bottom of the vessel G is placed a 3 to 4 inch 
deep layer of cupric oxide, 0, and the vessel is filled with a 
solution of 50 parts of caustic potash in 100 of water. When 
the cell is closed, decomposition of water takes place, the oxy- 
gen which appears on the zinc forming with the latter zinc 
oxide, which readily dissolves in the caustic potash solution, 
while the hydrogen is oxidized, and cupric oxide at the same 
time reduced to copper. When the cell is open, i. e., the 
circuit not closed, neither the zinc nor the cupric oxide is 



SOURCES OP CURRENT. 83 

attacked, and hence no local action nor any consumption of 
material takes place. The electro-motive force of this cell is 
0.98 volt, and its internal resistance very low. It is remark- 
ably constant, and is well adapted for electro-plating purposes 
by using two of them for one Bunsen cell. The following 
rules have to be observed in its use : It is absolutely necessary 
that the ebonite cover should hermetically close the vessel G, 
as otherwise the caustic potash solution would absorb carbonic 
acid from the air, whereby carbonate of potash would be 
formed, which would weaken the exciting action of the solu- 
tion. Further, the vessels G which form one of the poles must 
be insulated one from the other as well as from the ground, as 
otherwise a loss of current or defective working would be the 
consequence. 

The regeneration of the cuprous oxide or metallic copper 
formed by reduction from the cupric oxide to cuprous oxide, 
requires it to be subjected, to calcination in a special furnace. 
The expense connected with this operation is, however, about 
the same as that of procuring a fresh supply of cupric oxide. 
Lallande himself, as well as Edison, endeavored to bring the 
pulverulent cupric oxide into compact plates, but the regener- 
ation of these plates was still more troublesome. By treat- 
ment with various chemical agents, Dr. Bottcher, of Leipsie, 
has succeeded in producing porous plates of cupric oxide 
which, after subsequent reduction by absorption of oxygen 
from the air, can be readily re-oxidized to cupric oxide, but as 
far as we know of, cells with these plates have not been intro- 
duced into commerce. 

Cupron cell. The cell brought into commerce under this 
name by Umbreit & Matthes is a modification of the Lallande 
and Chaperon cell, it being furnished with a cuprous oxide 
plate. A square glass vessel or vat, furnished with a hard 
rubber cover, contains two zinc plates and between them the 
porous cuprous oxide plate. The glass vessel is filled with 20 
per cent, caustic soda solution, and the current is delivered by 
means of two binding screws on the outside of the cover. The 



84 ELECTRO-DEPOSITION OF METALS. 

zinc dissolves, zinc-oxide-soda being formed according to the 
following scheme, while the cuprous oxide is reduced to copper: 

Cuprous oxide 

CuO( + ) 




_ Zn{ONa). l 
Zinc oxide soda. 

The reduced positive pole plates are regenerated by rinsing 
in water and keeping them in a warm place for 20 to 24 hours, 
it being only necessary to replace the caustic soda solution 
which has become saturated with zinc oxide. The electro- 
motive force of the cell is 0.8 volt ; the standard current- 
strength, according to the size of the cells, 1, 2, 4, and 8 am- 
peres. Like the Lallande and Chaperon cell, this cell works 
without giving off any odor and the remarks regarding her- 
metical closing of the former also apply to the latter. An 
addition of sodium hyposulphite to the caustic soda solution is 
recommended as being productive of uniform wear and greater 
durability of the zinc plates. 

According to Jordis' investigations the use of potash lye 
with 15 per cent, potassium hydrate is more advantageous, as 
well to heat the plates for the purpose of regeneration to 
302° F. 

The elements of Marie, Davy, Naudet, Duchemin, Sturgeon, 
Trouville, and others, being of little practical value may be 
passed over. 

Plunge batteries. For constructive reasons only one fluid is 
used into which the zinc plates as well as the carbon plates 
dip, a solution of chromic acid prepared by dissolving 10 parts 
of potassium dichromate, or better sodium dichromate, and - 5 V 
part of mercuric sulphate in 100 parts of water, and adding 38 
parts of pure concentrated sulphuric acid, being employed. 



SOURCES OP CURRENT. 



85 



A plunge battery, as constructed by Fein, consists of a 
wooden box, which contains in two rows six vessels into which 
dip the zinc and carbon plates. The latter are secured to 
wooden cross-pieces furnished with handles, and may be 
maintained at any height desired by the notches in the stand- 
ards. According to the current-strength required the plates 
are allowed to dip in more or less deeply. 

In using the above-mentioned chromic acid solution origin- 

Fig. 15. 




ally recommended by Bunsen, the cells first develop a very 
strong current, which, however, in a comparatively short time 
becomes weaker and weaker. The current-strength can be in- 
creased by adding at intervals a few spoonfuls of pulverized 
chromic acid to the chromic acid solution, which, however, 
finally remains without effect, when the battery has to be 
freshly filled. Hence these batteries are not suitable for 



86 



ELECTRO-DEPOSITION OF METALS. 



Fig. 16. 



electro-plating operations requiring a constant current for some 
time, but they may be employed for temporary use. 

If plunge batteries are to be used for constant work in elec- 
tro-plating, it is preferable to use batteries with two acids, 
namely, dilute sulphuric acid and concentrated nitric acid, or 
chromic acid. 

In Stoehrer's construction (Fig. 15) the porous clay cup is 
omitted, the massive carbon cylinders K, K, etc., being each 
provided with a cavity reaching almost to the bottom which 

is filled with sand and nitric acid. 
The contact of the carbon and zinc 
cylinders is prevented by glass beads 
imbedded in the carbon cylinders. 

Fig. 16 shows a plunge battery 
manufactured by Dr. G. Langbein 
& Co., the details of which will be 
readily understood without further 
description. The zinc plates dip in 
the diaphragms, which are filled 
with a mixture of 26 lbs. of water 
and 2 lbs. of sulphuric acid free 
from arsenic, in which 2f ozs. of 
amalgamating salt have previously 
been dissolved. The carbon plates 
dip into the glass vessels, which 
contain a solution of commercial 
crystallized chromic acid in the pro- 
portion of 1 part acid to 5 water. 
In place of this pure chromic acid 
the following mixture may also be 
used : Water 10 parts by weight, 
sodium dichromate 1.5 parts by weight, pure sulphuric acid 
of 66° Be. 5 parts by weight. 

This solution shows no inclination towards crystallization. 
In the illustration only two cells are combined to a battery, 
but in the same manner a plunge battery of four or eight 




SOURCES OF CURRENT. 



87 



cells may be constructed, the separate cells of which may 
all be coupled parallel, as well as one after the other, and in 
mixed groups. 

Bichromate cell. For temporary use, for instance by gold- 
workers and others ; for gilding or silvering small articles, the 
bottle-form of the bichromate cell (Fig. 17) may be advantage- 
ously employed. In the bottle A two long strips of carbon 
united above by a metallic connection are 
fastened, parallel to one another, to a vul- 
canite stopper, and are there connected 
with the binding-screw ; these form the neg- 
ative element, and pass to the bottom of the 
bottle. Between them is a short, thick strip 
of zinc attached to a brass rod passing 
stiffly through the center of the vulcanite 
cork, and connected with the binding-screw. 
The zinc is entirely insulated from the 
carbon by the vulcanite, and may be drawn 
out of the solution by means of the brass 
rod as soon as the services of the cell are 
no longer required. 

Coupling cells. According to the laws of 
Ohm, previously discussed, the current- 
strength J of a cell is equal to its electro- 
motive force E divided by the sum of the internal resistance 
w and the external resistance wi : 

w + wi 
By now combining several such cells, say n cells, to a bat- 
tery, the electro-motive force of the latter will become n.E, 
but the internal resistance n.w, and with the same closed cir- 
cuit as the single cell had, the external resistance wi will not 
increase. Hence the current-strength of these n elements has 
to be written 

n.E 




J = 



n.w. + wi 



00 ELECTRO-DEPOSITION OF METALS. 

Now it is evident that, if a definite closed circuit with a 
resistance of wi be given, the current-strength cannot be 
indefinitely raised by increasing the number of n elements. 
While with an increase in the number of n elements, the electro- 
motive force to be sure grows as many n times, the internal 
resistance, w, also grows, so that finally the value wi which 
remains the same disappears for the resistance nw which in- 
creases n-times. Thus the current-strength approaches more 
and more the limit of value 

E? == E 
nw w 

On the other hand, the effect can neither be increased at will 
by enlarging the surface of the pair of plates or decreasing the 
conducting resistance of the fluid in a given number of cells. 
Because if wi — the external resistance — is large enough so 
that the internal resistance nw may be disregarded, the current- 
ly 
strength approaches more and more the value — 

wi 

Hence, it follows that the enlargement of the surface of the 
exciting pair of plates produces an increase in the current-strength 
only when the external resistance in the closed circuit is small in 
proportion to the internal resistance of the battery. 

If we now apply the results of the above explanations to 

Fig. 18. 

*fa Vfa V^CD Vmzd V= 

practice, we find that the cells may be coupled in various 
ways according to requirement. 

1. If, for instance, four Bunsen cells (carbon-zinc) are 
coupled one after another in such a manner that the zinc of one 
cell is connected with the carbon of the next, and so on (Fig. 
18), the current passes four times in succession through an 



SOURCES OP CURRENT. 



89' 



equalty large layer of fluid, in consequence of which the in- 
ternal resistance (4w), is four times greater than that of a 
single cell, while the resistance of the closed circuit (wi), re- 
mains the same. Hence, while the current-strength is thereby 
not increased, the electro-motive force is, and for this reason 
this mode of coupling is called the union or coupling of the 
elements for electro-motive force or tension. 

Fig. 19. 




Fig. 20. 



2. By connecting four cells alongside of each other, i. e., all 
the zinc plates and all the carbon plates one with another 
(Fig. 19), the current simultaneously passes through the same 
layer of fluid in four places ; the internal resistance of the 
battery is therefore the same as that of 
a single cell, and since the surface of 
the plates is four times as large as 
that of a single cell, the quantity of 
current is increased by this mode of 
coupling. This is called coupling for 
quantity of current, or coupling in parallel. 

3. Two cells may, however, be con- 
nected for electro-motive force or ten- 
sion, and several such groups coupled 
alongside of each other, as shown in 
Fig. 20, whereby, according to what 

has above been said, the electro-motive force, as well as the 
current-strength, is increased. This mode of connection is 
called mixed coupling, or group coupling. 

According to the resistance of the bath as the exterior closed 
circuit, and according to the surfaces to be plated, the electro- 




90 



ELECTRO-DEPOSITION OF METALS. 



plater may couple Lis cells in either way. We will here only 
mention the proposition deduced from Ohm's law, that a num- 
ber of voltaic cells yield the maximum of current-quantity when 
they are so arranged that the internal resistance of the battery is 
equal to the resistance in the closed circuit. Hence, when oper- 
ating with baths of good conductivity and slight resistance, 
for instance, acid copper baths, silver cyanide baths, etc., with 
a slight distance between the anodes and the objects, and with 
a large anode-surface, it will be advantageous to couple the 
elements alongside of each other for quantity. However, for 
baths with greater resistance and with a greater distance of 
the anodes from the objects, and with a smaller anode surface, 
it is best to couple the elements one after the other for electro- 
motive force or tension. 

B. Thermo-Electric Piles. 
Although thermo-electric piles are only used in isolated 

Fig. 21. 




cases for electro-plating operations, for the sake of complete- 
ness their nature and best-known forms will be briefly men- 
tioned. 

Professor Seebeck, of Berlin, observed in 1823, that elec- 



SOURCES OF CURRENT. 



91 



tricity is developed when the soldered joints of two metals are 
unequally heated ; hence, while electricity can be converted 
into heat, heat vice versa can be converted into electricity. 

Noe's thermo-electric pile (Fig. 21) consists of a series of 
small cylinders composed of an alloy of 36 J parts of zinc and 
62 J parts of antimony for the positive element and stout Ger- 
man silver as the negative element. The soldering consists 
of tin. The junctions of the elements are heated by small gas 
jets, and the alternate junctions are cooled by the heat being 
conducted away by large blackened sheets of thin copper. A 
pile of twenty pairs has an electro-motive force of 1.9 volts. 

Clamond's thermo-electric pile (Fig. 22) also consists of a zinc- 

Fig. 22. 




antimony alloy, but in place of German silver, ordinary 
tinned sheet iron is employed. To insure good contact be- 
tween the two metals, a strip of tin-plate is bent into a narrow 
loop at one end. This portion is then placed in a mould and 
the melted alloy poured around it, so that it is- actually 
imbedded in the casting. The pile shown in the illustration 
consists of five series, one placed above the other. Each series 
has ten elements grouped in a circle, and is insulated from the 



92 



ELECTRO-DEPOSITION OF METALS. 



succeeding series by asbestos disks. With the consumption of 
about 6 J cubic feet of gas per hour, such a pile deposits 0.7 oz. 
of copper, which corresponds to an intensity of about 17 
amperes. 

Quicker' s thermo-electric pile, invented in 1890, is shown in 
Fig. 23. It is arranged for gas-heating, and with a constant 
supply of gas requires a pressure-regulator. The negative 
electrodes consist of nickel, and the positive electrodes of an 
antimony alloy, the composition of which is kept secret. The 
negative nickel electrodes have the form of thin tubes and are 
secured in two rows in a slate plate, which forms the termina- 
tion of a gas conduit with a U-shaped cross-section beneath it. 
Corresponding openings in the slate plate connect the nickel 

Fig 23. 




tubes with the gas conduit, the latter being connected by means 
of a rubber tube with the pipe supplying the gas. Thus the 
gas first passes'jnto the conduits, next into the nickel tubes, and 
leaves the latter through six small holes in a soapstone socket 
screwed in the end of each tube. On leaving these sockets the 
gas is ignited and the small blue flames heat the connecting 
piece of the two electrodes. This connecting piece consists of 
a circular brass plate placed directly over the soapstone socket. 
One end of it is soldered to the nickel tube, while the other 
end, towards the top, is in a socket in which are cast the posi- 
tive electrodes. The latter have the form of cylindrical rods with 
lateral angular prolongations. To the ends of these prolonga- 



SOURCES OF CURRENT. 93 

tions are soldered long copper strips secured in notches in the 
slate plate. They serve partially for cooling off and partially 
for connecting the couples. For the latter purpose each cop- 
per strip is connected by a short wire with the lower end of the 
nickel tube belonging to the next couple. When the pile is to 
be used, the gas is ignited in one place, the ignition spreading 
rapidly through the entire series of couples. In about 10 min- 
utes the junctions of the metals have attained their highest 
temperature and the pile its greatest power, which, with a con- 
stant supply of gas. remains unchanged for days or weeks. 

In view of the conversion of the heat produced by the com- 
bustion of the gas into electricity, the useful effect of the 
thermo electric pile can be considered only a very slight one. 
One cubic meter of ordinary coal-gas produces on an average 
5200 heat-units, hence 200 litres per hour referred to one 
second l-eVI- 5200 = 0.20 heat-unit. These correspond to 
1208 volt-amperes, 1 volt-ampere being equal to 0.00024 heat- 
unit. Hence, in Giilcher's thermo-electric pile, which of all 
known thermo-piles produces the* greatest useful effect, not 
much more than 1 per cent, of heat is utilized in the entire 
circuit, and about \ per cent, in the outer circuit. 

Although thermo-electric piles may be, and are occasionally, 
used for electro-plating operations, they cannot compete with 
dynamo-electric machines driven by steam, which as regards 
the consumption of heat are at least five times more effective. 
They can only be used in place of voltaic batteries, having 
the advantage of being more convenient to put in operation, 
more simple, cleanly, odorless, and requiring less time for 
attendance. But, on the other hand, their original cost is 
comparatively large, it being ten to twenty times that of 
Bunsen cells. 

C. Dynamo-Electric Machines. 

While in the voltaic cells, chemical energy is converted 
into electric energy, and in the thermo-piles, heat into elec- 
tricity, in the dynamo-electric machine a conversion of me- 
chanical energy into electrical energy takes place. 



94 



ELECTRO-DEPOSITION OE METALS. 



Fundamental principle of dynamo-electric machines. In the 
dynamo-electric machines the generation of the current results 
from induction, and the fundamental principle of such a 
machine is as follows : 

Suppose an iron magnet frame M, formed of a powerful 
horse-shoe magnet, which is provided with two cylindrically- 
turned planes, and concentrically fixed to these planes, a 
cylinder A, built up of discs of soft iron as shown in Fig. 24. 

Fig. 24. 




Lines of force running in the direction from the north pole 
to the south pole permeate the soft-iron cylinder. If in the air- 
space between the north pole of the magnet and the cylinder, 
a copper wire, indicated in the illustration by a small circle, 
be introduced, and moved in such a manner that it cuts the 
lines of force flowing from the north pole through the air- 
space to the cylinder, a current is induced, and a certain 
electro-motive force appears at the ends of the wire. By 
moving the left-hand wire in the direction indicated by the 



SOURCES OF CURRENT. . 95 

arrow, the current, according to the hand rule illustrated by 
Fig. 4 will flow away from the observer into the plane of the 
illustration, and by moving the right-hand wire in the direc- 
tion of the arrow, out from the plane of the illustration to- 
wards the observer. 

Instead of moving the wire in the air-space, it may also be 
insulated from the soft-iron cylinder and secured to it. If now 
the cylinder be moved around its axis, the wire cuts the lines 
of force in exactly the same manner as in its motion in the 
air-space, the effect remaining the same. If several wires, one 
alongside the other, be secured upon the cylinder, a corre- 
sponding electro-motive force will be produced on the ends of 
each wire, the positive poles of the wires being then on one 
side, say the front, of the pole pieces, while the negative poles 
of all the wires lie upon the other, the rear, side. If now the 
wires be connected one with the other, so that, when the 
cylinder is revolved, a' positive pole is always attached to a 
negative pole, the electro-motive force is raised in the same 
degree as the number of wires coupled one after the other (in 
series) increases. 

These wires fastened upon the iron body are called windings,. 
and the term armature is applied to an iron body furnished 
with such windings. 

The electro-motive force generated in the windings is the 
greater, the greater the velocity with which the wires, or con- 
ductor forming the windings, are moved through the mag- 
netic field. If the length of the conductors be increased by 
enlarging the windings, and the velocity with which the 
armature moves remains the same, the electro-motive force 
generated in the conductor is proportional to the length of the 
latter. If, on the other hand, the magnetic field be strength- 
ened, thus increasing the lines of force cut by the conductor 
during its motion, and the velocity with which the conductor 
moves, as well as its length, remains the same, the electro- 
motive force is proportional to the number of lines of force, 
reaching its greatest value when the lines of force are perpen- 
dicularly cut by the conductor. 



■yt> 



ELECTRO-DEPOSITION OF METALS. 



Separate parts of the dynamo- electric machine. The frame. 
The production of the magnetic field has for a long time been 
effected by electro-magnets. The field magnets of gray cast- 
iron or cast-steel are cast in one piece with the gray cast-iron 
or cast-steel frame, or screwed to it. These field magnets are 
wrapped with wire through which the current, by which they 
are magnetically excited, is conducted. This winding • is 
called magnet winding or field winding. According to the 
number of field magnets, a distinction is made between two- 
polar, four-polar, six-polar and multipolar machines. 

Fig. 25 shows a two-polar, and Fig. 26 a four-polar type of 



Fig. 25. 



Fig. 26. 





dynamo of the firm of Dr. G. Langbein & Co., Leipsic, Ger- 
many. The frame and foundation plate of soft cast-iron are 
cast in one single casting ; only in larger types is the frame 
secured to the foundation plates by screws. 

For the production of the magnetic field, the current was 
formerly conducted from another source of electricity into the 
magnet windings, but since the discovery of the dynamo- 
electric principle by W. v. Siemens, the electric current gener- 
ated in the armature is utilized for the excitation of the mag- 
netic field. The dynamo-electric principle is based upon the 
following : Lines of force, few in number, are present from a 
jprevious excitation in every magnet frame, and this is called 



SOURCES OP CURRENT. 97 

remanent magnetism (see p. 13). In revolving the armature 
the existence of this small number of lines of force suffices for 
the induction of a weak current which is partly conducted 
through the magnet winding, the magnetic field being thereby 
intensified. The effect of this is the generation of currents of 
considerably greater power in the armature, which again bring 
about an increase in the current-strength in the magnet wind- 
ing, until the frame is saturated with lines of force. This 
process is called self-excitation, while the term foreign or sepa- 
rate excitation has- been applied to it when the magnetic field 
is excited by another source of electricity. 

Armature or inductor. It has already been mentioned that 
the armature consists of a cylindrical iron body and the wind- 
ings wrapped around it. The iron body cannot be made of one 
piece because rotatory currents would be formed in it, which 
heat the iron very much, and cause a loss of current. Hence 
the body of the armature is built up of thin, soft sheet-iron 
■discs insulated one from the other by discs of paper. The 
•discs are firmly pressed upon the core of the armature and 
secured by screws, while the core of the armature itself is 
wedged upon the shaft by means of a wedge. 

According to the manner in which the wire windings are 
laid around the armature-core, a distinction is made between 
•a ring armature and a drum armature. 

In the ring armature the wire windings are wrapped in a 
■continuous spiral around the armature-core, it being necessary 
for the latter to have a wide bore in the center through which, 
in wrapping, the conducting wire may be carried. Fig. 27 
represents a scheme of such ring-winding. iVand S are the 
two field magnets of the frame. Every two of the continuous 
wire windings represent a coil, and from the point where the 
•end of one coil is connected with the commencement of the 
next coil a conducting wire branches off to the collector. 
According to what has above been said, induction is greatest 
when the windings of the wire cut the lines of force at a right 
•angle, this being the case when the windings are directly 
7 



98 



ELECTRO-DEPOSITION OF METALS. 



under the poles. In revolving the armature from 0° to 90°, 
the generation of current decreases, from 90° to 180° it de- 
creases, from 180° to 270° it increases in a reverse sense, and 
from 270° to 300° it again decreases. Thus, currents flowing 
alternately in opposite directions, the so-called alternating 
currents are generated, and their conversion into constant 



Fig. 27. 




ISO. 



currents of uniform direction is effected by the commutator. 
At 0° and at 180°, the generation of current is equal to 0, 
and at these points the current changes its direction ; the line 
0° to 180° is called the neutral zone. 

In the drum armature the conducting wires are wound upon 
the armature-core parallel to its axis, carried on the faces of 
the core around the core-shaft, and the ends of every two coils 



SOURCES OF CURRENT. 



99 



lying alongside each other on a face are connected, one with 
the other, and with a segment of the commutator. 

Fig. 28 shows the drum winding viewed from the side of 
the commutator. Each coil is only indicated by a single wire 
winding, and therefore 8 coils are shown. The full lines 
indicate the connection of the coils upon the commutator-side 

Fig. 28. 




and with the commutator, and the dotted lines, the coil-con- 
nections upon the opposite face. 

What has been said in regard to the intensity of induction 
in ring-armatures applies also to drum-armatures. 

The chief difference between the modes of winding consists 
in more wire being required for ring winding, because wires 



100 ELECTRO-DEPOSITION OF METALS. 

run on the faces as well as in the interior of the bore, which 
are of no importance as regards the generation of the current 
by induction, but, on the one hand, materially increase the 
weight of the armature, and, on the other, enlarge the resist- 
ance. As regards these points, drum-winding has much in its 
favor, and it has the further advantage that the armature-core 
can be provided, parallel to its axis, with grooves or slots for 
the reception of the windings, they being thus better protected 
from injury, and the effect of centrifugal force can in a suit- 
able manner be prevented by bands. In such armatures, even 
when equipped with thick copper wires or flat copper bands, 
scarcely any rotatory currents are generated, because the slots 
are but slightly permeated with lines of force, the latter run- 

Fig. 29. 



ning rather around the copper wires through the iron. How- 
ever, the chief advantage of such an armature consists in that 
the air-space between armature and magnet-pole can be less 
than in armatures with windings not placed in slots, because 
the space occupied by the winding of such so-called smooth 
armatures has to be considered as an air-space and offers the 
greater magnetic resistance. Hence for armatures furnished 
with slots, the number of ampere-windings may be less than 
for smooth amatures. Fig. 29 shows a slotted armature of a 
dynamo constructed by the firm of Dr. G. Langbein & Co., in 
which the conductors consist of flat copper rods, connected on 
the faces by bent copper bands called evolvents. 

Commutator. This is a cylindrical body built up of seg- 
ments and fastened to the armature-shaft. It is insulated 



SOURCES OF CURRENT. 101 

with mica. The segments consist of copper, tombac, or brass 
and are insulated from each other as well as from the com- 
mutator frame, i. e., the iron body. The commutator has as 
many segments as the armature has coils, and every point of 
junction of two coils is intimately connected by means of 
copper ,with a segment. The function of the commutator 
consists in converting the alternating currents of the windings 
generated by induction into constant currents of uniform 
direction. As seen from Fig. 27, currents of opposite direc- 
tions flow in each half of the windings of the ring-armature. 
If now sliding contacts be placed on the commutator on the 
points of the neutral zone, the current of one-half of the wind- 
ings is carried along as positive current by one of the sliding 
contacts, and the negative current of the other half by the 
other sliding contact. The armature winding is divided into 
two halves by the brushes which are coupled parallel to each 
other. The induction of each separate coil corresponds to its 
position for the time being in the magnetic field, the sum of 
the induction of all the coils in one-half of the armature being 
equal to that of all the coils in the other half, but as previ- 
ously shown, the direction of the current in both halves is 
different. 

Brushes. The function of the brushes is to take off the cur- 
rent from the commutator. For such dynamo-electric ma- 
chines as here come into question, the brushes are of fine 
copper or brass wire-gauze, or of very thin metal-plate. Car- 
bon brushes are often used for dynamo-electric motors. 

The choice of material for the brushes depends on the prop- 
erties of the material of the commutator. As there should be 
as little wear as possible of the commutator by the brushes, 
the material used for the latter should be somewhat softer 
than that for the former. Copper and brass gauze brushes 
produce by their wear considerable metallic dust, which settles 
on all parts of the machine, as well as on the armature and, 
if not removed by frequent blowing out with a pair of bellows, 
or a similar instrument, may readily cause short-circuiting. 



102 ELECTRO-DEPOSITION OF METALS. 

Brushes of twisted, thin inetal-plates (Boudreaux brushes) do 
not show this disagreeable formation' of dust, and cause but 
little wear of the commutator, rather polishing it. They 
have, however, the drawback of the portions bearing on the 
commutator oxidizing readily, in consequence of becoming 
heated by the large quantities of current. This oxidation is 
not removed by the friction, and greater resistance is thereby 
opposed to the passage of the current from the commutator to 
the brushes. This, on the one hand, results in the commu- 
tator and brushes becoming strongly heated and, on the other, 
causes a decrease in taking off the current. 

The bearing surfaces of the brushes should be so large that 
no heating is caused by the passage of the current, which 
would increase to a considerable extent the quantity of heat 
unavoidably formed by the friction, and be a disadvantage as 
regards the useful effect of the dynamo. 

Brush-holders. These serve for securing the brushes and 
should hold them so as to bear with an even pressure upon 
the commutator. This is effected by metal springs by means 
of which the brush-frame, which carries the brush, is elas- 
tically connected with the portion of the brush-holder screwed 
to the bolt of the brush-rocker. 

Brush-rocker. This serves for carrying the brush-holder, 
and for this purpose is furni shed with two thick copperbolts 
having a cross-section corresponding in size to the quantity of 
current to be conducted. In multi-polar dynamos, the rockers 
are equipped with as many bolts as there are poles. These 
bolts are insulated from the rocker by cases of a good insu- 
lating material, and secured to the rocker by insulated nuts. 

The rocker is mounted upon the turned end of a bearing, 
and is concentrically movable to its axis, so that by turning 
it, the brushes may be shifted into a position at which the 
dynamo runs with the least sparking. In this position the 
brush holder is kept by means of an adjusting screw. 

The rocker should also be kept free from metal dust, other- 
wise short-circuiting may readily result. 



SOURCES OF CURRENT. 103 

The other parts of a dynamo, such as bearings, cable, etc., 
need not be especially referred to, and it only remains to dis- 
cuss the various types of 

Direct current dynamos. If the whole of the current traverses 
the coil of the field magnet, the dynamo is said to be series 
wound ; or if a portion of the current be shunted we have a 
shunt-wound dynamo ; or finally there may be a combination 
of the two in which, case the machine is a compound dynamo. 
Whatever be the arrangement, provided the volume of the 
copper and the density of the current are the same, the same 
field is always produced. 

Nearly all the early types of electric dynamos were what is 
known as " series wound " machines, where the full current of 
the armature passed through the field coils. These machines 
had the very serious disadvantage of possessing poor regula- 
tion and being subject to frequent reversal of current direc- 
tion. The plating dynamos on the market to-day are what 
is technically known as "shunt-wound" and "compound- 
wound " machines. 

In a shunt-wound dynamo the field magnet coils are placed 
in a shunt to the armature circuit so that only a portion of 
the current generated passes through the field magnet coils, 
but all the difference of potential of the armature acts at the 
terminals of the field circuit. 

In a shunt-wound dynamo, an increase in the resistance of 
the external circuit increases the electro-motive force, and a 
decrease in the resistance of the external circuit decreases the 
electro-motive force. This is just the reverse of the series- 
wound dynamo. 

In a shunt-wound dynamo a continuous balancing of the 
current occurs. The current dividing at the brushes between 
the field and the external circuit in the inverse proportion to 
the resistance of these circuits, if the resistance of the external 
circuit becomes greater, a proportionately greater current 
passes through the field magnets, and so causes the electro- 
motive force to become greater. If, on the contrary, the re- 



104 



ELECTRO-DEPOSITION OF METALS. 



sistance of the external circuit decreases, less current passes 
through the field, and the electro-motive force is proportion- 
ately decreased. Thus, up to a certain degree, a shunt-wound 
dynamo regulates itself. 

Fig. 30 illustrates a two-pole shunt-wound dynamo, and 
Fig. 31 a two-pole shunt-wound dynamo for high current- 
strengths. 

In Fig. 30 the frame is of cast-steel and the bearing plates 
are screwed to it. In Fig. 31 the pillow-blocks and frame are 
mounted upon a common cast-iron plate. . 

The armature is of the slotted drum type described in 

Fig. SO. 




Fig. 29. It is encompassed by two strong field magnets 
arranged in vertical position, radially opposite one to the other. 
The ends of the field magnets are concentrically turned to the 
armature and their oblique tapering shape prevents the jerky 
formation or interruption of the current, thus rendering possi- 
ble a sparkless taking-off of current on the commutator. The 
ends of the armature coils are soldered to the copper segments 
of the commutator, loosening of the connecting points being 
thus excluded, as is invariably the case with wires secured by 
means of screws to the commutator. An abundance of cop- 
per cross-sections being used, the degree of efficiency of the 
dynamo is an excellent one. To decrease friction, the portions 



SOURCES OF CURRENT. 



105- 



of the steel armature shaft which run in the journal boxes of 
phosphor-bronze, as well as the latter themselves, are highly 
polished. The bearings are furnished with automatic ring- 
lubrication. By reason of the use of large cross-sections of 
copper .upon the armature and magnet winding, the number 
of revolutions is a moderate one, and consequently the con- 
sumption of power and wear of the bearings are slight. 

Dynamos which yield high current-strengths are furnished 
with two commutators to avoid overloading and consequent 
excessive heating of a single commutator. 

Fig. 31. 




A compound wound dynamo has two distinct windings on 
its field magnet — one of the very many turns of fine wire, 
called the shunt winding, and another known as the series 
winding, which latter consists of a number of turns of heavier 
gauge wire. The series winding is in series with the vats or 
external circuit. The current that is used in the vats, pass- 
ing through this winding, increases the magnetism of the field 
as the load increases, and thus the drop in voltage, which 
would otherwise occur by reason of the increased drop in the 
armature winding and increased magnetic reaction caused by 
the armature current is provided for. 



106 ELECTRO-DEPOSITION OF METALS. 

Fig. 32 shows a multi-polar type of "dynamo manufactured 
by The Hanson & Van Winkle Co., Newark, N. J. The 
frame is made of a high-grade cast iron, having a high mag- 
netic permeability. The poles are made of soft rolled steel 
with cast-iron shoes. Field coils are of insulated copper wire 
wound compactly by machinery, insuring the maximum 
ampere-turns without great bulk. The whole coil is properly 
insulated and protected from mechanical injury. 

Fig. 32. 




The armature, Fig. 33, is of the toothed type. The core is 
built up of thin soft steel discs, and is insulated on both sides 
smd assembled on a spider constructed to insure the greatest 
-amount of ventilation. 

The armature coils are made in a form and perfectly insu- 
lated. The slots in which the coils rest are also insulated, so 
that there is no chance for a ground. 

The segments of the commutator are forged from pure cop- 
per carefully insulated with the best mica. The radials from 
the bars are so set that a steady current of air is thrown on 
(the commutator and brushes. 



SOURCES OF CURRENT. 



107 



The bearings are self-aligning, boxes are made of special 
bronze, and are provided with large oil-wells and automatic 
oiling-rings. 

Fig. 33. 




This machine will run continuously under full load with a 
rise of temperature above the surrounding atmosphere not 



Fig. 34. 




exceeding 55° F. in the accumulator, and something less in 
windings. 



108 ELECTRO-DEPOSITION OF METALS. 

. Fig. 34 shows a separately excited dynamo of the multi- 
polar type manufactured • by The Hanson & Van Winkle Co., 
Newark, N. J. It is a very popular form of generator, the- 
field being excited from an external circuit, usually 1 10 or 
220 volts D. C. The capacity is 4000 amperes at 6 volts. 
The commercial efficiency is high, 86 per cent. — the electrical 
efficiency averages 93 per cent. This form of dynamo is fur- 
nished for both two and three wire systems of current distribu- 
tion. The frame and pole pieces are of steel. For the frame 
a special, soft grade is used, having a high magnetic perme- 
ability. The field coils are made of insulated copper wire 
wound compactly by machinery, insuring the maximum 
ampere-turns without great bulk. The whole coil is properly 
insulated and protected from mechanical injury. 



The great advance which has in modern times been made 
in the art of electro-plating, is largely due to the important 
improvements that have been made in the construction of 
dynamo-electric machines, by which mechanical energy gener- 
ated by the steam-engine or other convenient source of power 
may be directly converted into electrical energy. Without 
dynamos it would be impossible to electro-plate large parts of 
machines, architectural ornaments, etc., which are thus pro- 
tected from the influence of the weather. They may safely be 
credited with having called into existence an important branch 
of the electro-plating art, viz., nickel-plating, and especially 
the nickel-plating of zinc sheets, as well as sheets of copper, 
brass, steel, and tin, which would have been impossible if the 
manufacturer had to rely upon the generation of the electric 
current by batteries. The latter, at the very best, are trouble- 
some to manage ; they only give out their full power w T hen 
freshly charged, and as the chemical actions upon which they 
rely for their power progress, they deteriorate in strength and 
require frequent additions of acids and salts to be freshly 
charged, and their use demands constant vigilance and atten- 
tion. Even when working on a small scale, it is cheapest to 



SOURCES OF CURRENT. 109 

procure a small gas or other motor for driving a small dynamo, 
the lathes, and grinding and polishing machines. 

Most cities and towns are now supplied with electric light 
from central stations, and thus the means are furnished to 
smaller plants to avail themselves of the use of electricity 
without the necessity of installing their own source of power. 
From such central stations the conductors are fed with cur- 
rents of 110 or 220 volts. Hence the wires from the power 
circuit can be directly connected with a motor-generator, 
which is constructed for the respective voltage and converts 

Fig. 35. 




the supply of current into power, driving, for instance, a 
connecting gear, from which the grinding and polishing 
machines, as well as a dynamo of low voltage, are impelled. 
The dynamo may be directly connected by means of a flexible 
•or rigid coupling to the motor-generator. The armature of 
the latter may also be directly placed upon the grinding and 
polishing shafts, and the magnets arranged around it, so that 
every working machine becomes a motor-generator. 

Fig. 35 shows a 150-ampere motor-generator set, and Fig. 
36, a 4000-ampere motor-generator set, manufactured by The 
Hanson & Van Winkle Co., Newark, N. J. A low voltage 
•dynamo is directly connected to a motor of suitable size, the 



110 



ELECTRO-DEPOSITION OF METALS. 



whole outfit being mounted on a substantial iron base. There 
is no loss of power as in the caee when belts are used, so the 
full capacity of the generator is available. In many instances 
the plating dynamo is installed some distance from the tank,, 
and conductors of large cross-sections must be used in order 
that there may be no drop in voltage at the tanks. Th is,of 
course, increases the cost of installation. With the motor- 

Fig. 36. 




generator set, wires from the power-circuit can be brought to 
the plating room and the outfit can be set up near the tanks. 
These outfits are made in all sizes, both bipolar generators, as 
shown in the illustration, or generators of the multipolar type 
being used. 

To enable the manufacturer of dynamos to suggest the most 
suitable machine the following data should be submitted to 
him: 

1. Variety, size, and number of the baths which are to be 
fed by the machine. 

2. The average surface of the articles in the bath, or their 
maximum surface, and the metals of which they consist. 



SOURCES OF CURRENT. Ill 

3. Whether at one time many, and at another time few,, 
articles are suspended in the bath. 

4. The distance at which the machine can be placed from, 
the baths. 

5. The power at disposal. 

If the establishment is to be electrically-driven by a motor- 
generator, the machines which, in addition to the dynamo, 
are to be driven by the motor-generator should be mentioned, 
as well as the voltage of the power-circuit which is to be used 
as a supply of electricity. 

D. Secondary Cells (Accumulators). 

In the theoretical part of this treatise, the polarization- 
current has been referred to. Although the polarization of 
metal plates for the production of secondary currents had 
previously been employed by Ritter, the construction of prac- 
tically useful accumulators was first accomplished by Plante. 
He found that lead plates dipping in dilute sulphuric acid 
were specially well adapted for the production of secondary 
currents, and he arranged the accumulators as follows: In a 
square glass vessel filled with 10 per cent, sulphuric acid solu- 
tion, a large number of lead plates were suspended in such a 
way that all plates with even numbers, 2, 4, 6, and so on, 
were electrically connected one with the other, while the plates 
with uneven numbers, hence, 1, 3, 5, and so on, were also in 
contact with each other. Between the separate plates dipping 
in the acid was sufficient space to prevent them from touch- 
ing one another. One series of the plates served as positive, 
and the other as negative, electrodes. Now by conducting an 
electric current through the plates, lead peroxide is formed 
upon the positive electrodes, and by interrupting the current 
and combining the series of electrodes with each other, the 
peroxide is reduced to metallic lead, and the negative lead 
plates are oxidized, whereby an electric discharge takes place, 
the secondary or accumulator-current passing through the 
metallic connection of the series of plates from the peroxide 
to the lead plates. 



112 ELECTRO-DEPOSITION OF METALS. 

Hence, in charging, a conversion of electrical energy into 
chemical energy takes place and, in discharging, a recon- 
version of the chemical energy into electric energy. A large 
quantity of the latter can therefore accumulate in the cells, 
whence the term accumulator is derived. 

For the production, in the above-described manner, of cur- 
rents of high power and longer duration, the plates have to be 
suspended as closely together as -possible without danger of 
contact, in order to decrease the internal resistance of the 
element as far as practicable, and also to increase the quantity 
of lead peroxide. 

However, the formation of the layer of lead peroxide upon 
the lead plates of Plante's accumulator was a slow process, and 
for this reason Faure used lead grids. The square openings 
in the negative plates are filled with a paste of litharge and 
sulphuric acid, and the positive plates with one of minium 
and sulphuric acid. The current reduces the litharge and 
peroxidizes the minium. 

Plante showed that accumulators form by usage — that is to 
say, that up to a certain point their capacity is greater the 
more frequently they have been charged and discharged. By 
repeated oxidation and deoxidation the lead acquires a spongy 
structure, and gradually a large mass of metal takes part in 
the reaction. The formation is accelerated by immersing the 
fresh plate for a day. or two in nitric acid diluted with its own 
volume of water. 

Chemical processes in the accumulator. Regarding these pro- 
cesses, several theories have been advanced, for instance, by 
Elbs, Liebenow, and others, but it has not yet been definitely 
settled which of these views is correct. There can, however, 
be no doubt that the lead sulphate which is formed by the 
action of the sulphurie acid upon the lead, plays the principal 
role, in so far as the charging and discharging of the accumu- 
lator are effected only by the decomposition and subsequent 
reformation of the lead sulphate. 

Elb's theory is as follows : As lead is bivalent and quadri- 



SOURCES OF CURRENT. 113 

valent, after the decomposition of the lead sulphate to lead 
and sulphuric acid, the latter combines with the lead sulphate, 
which remains undecomposed, to lead disulphate. This for- 
mation of lead disulphate must chiefly take place on the posi- 
tive electrodes, since the anion (the sulphuric acid residue) 
migrates to the positive pole, and by the action of the water 
the lead disulphate is decomposed to lead peroxide and free 
sulphuric acid. 

If, therefore, the current taken from a dynamo be conducted 
into the electrodes of an accumulator, so that the positive 
plates are connected with the + pole of the dynamo and the 
negative plate with the — pole, decomposition of sulphuric 
acid takes place, the hydrogen migrating to the negative elec- 
trode, and the sulphuric acid residue to the positive electrode. 
On the latter, the sulphuric acid residue forms first of all with 
the lead, lead sulphate according to the following equation : 

S0 4 + Pb = PbS0 4 

Sulphuric acid residue. Lead. Lead sulphate. 

By the influx of additional S0 4 -ions, this lead sulphate is 
converted into lead disulphate : 

S0 4 + PbS0 4 = Pb(S0 4 ) 2 

Sulphuric acid residue. Lead sulphate. Lead disulphate. 

However, since the formation of the lead disulphate does 
not take place quantitatively, S0 4 -ions are simultaneously con- 
verted into sulphuric acid, H 2 S0 4 , oxygen being separated in 
the form of gas. 

According to Elbs, lead disulphate decomposes with water 
to lead peroxide and sulphuric acid according to the following 
equation : 

Pb(S0 4 ) 2 + 2H 2 = Pb0 2 + 2H 2 S0 4 

Lead disulphate. Water. Lead peroxide. Sulphuric acid. 

Thus, if the current be interrupted, we have lead peroxide 
«on the positive electrode, and spongy lead reduced by hydro- 



114 ELECTRO-DEPOSITION OP METALS. 

gen, on the negative electrode. If now the positive electrodes 
be connected with the negative electrodes by a closed wire, a 
current passes through this wire from the positive lead per- 
oxide electrodes to the negative lead electrodes, and from the 
latter, through the electrolyte, back to the positive electrodes. 

Thus during the discharge, the spongy lead plate becomes 
the positive electrode and the lead peroxide plate, the nega- 
tive electrode, in consequence of which, by the decomposition 
of the sulphuric acid, the anion S0 4 migrates to the positive 
lead electrode, and forms lead sulphate, while the hydrogen 
separated on the negative electrode reduces the lead peroxide 
to lead oxide or to metallic lead. 

These processes take place according to the following equa- 
tions : 

On the -electrode Pb + S0 > . = PbS0 ' 

Lead. Sulphuric acid residue. Lead sulphate. 

On the + electrode Pb0 * . + 2H = Pb0 + H *° 

Lead peroxide. Hydrogen. Lead oxide. Water. 

This lead oxide formed on the + electrode also forms lead 
sulphate with sulphuric acid, and when all the lead peroxide 
is reduced, the generation of current ceases, the accumulator 
is exhausted, and has to be recharged, whereby a repetition of 
the processes above described takes place. On the spongy 
lead plate which has now again become the negative electrode, 
the lead sulphate formed is reduced by the hydrogen to spongy 
lead and sulphuric acid : 

PbS0 4 + 2H = Pb + H 2 S0 4 

Lead sulphate. Hydrogen. Lead. Sulphuric acid. 

whilst on the positive electrode lead peroxide is formed accord- 
ing to the above-described transpositions. 

From these processes it follows that by the discharge of the 
accumulator, sulphuric acid for the formation of lead sulphate 
is fixed on the negative, as well as on the positive, electrode. 
The electrolyte must therefore contain less free sulphuric acid 



SOURCES OF CURRENT. 115 

than at the time of charging, during which the lead sulphate at 
the negative electrode is reduced to lead, and oxidized to lead 
peroxide on the positive electrode, the sulphuric acid of the 
sulphate being thus again present in the electrolyte in the form 
of free sulphuric acid. The specific gravity of the electrolyte 
will be the higher, the more free sulphuric acid is present, and 
by determining it by means of a hydrometer it can be seen 
when charging is finished, the latter being the case when no 
further increase in the specific gravity is noticed. The com- 
pletion of charging is further indicated by a copious escape of 
oxygen on the positive pole plates, which is due to the sul- 
phuric acid residue finding no more material for the formation 
of lead sulphate, therefore forms sulphuric acid, water being 
decomposed, while oxygen in the form of gas is liberated. 

Liebenow assumes that in charging there are formed by the 
decomposition of the lead sulphate, sulphuric acid-ions, lead- 
ions, and, by the co-operation of water, lead peroxide-ions and 
hydrogen-ions, according to the following equation : 

2PbS0 4 + 2H 2 = Pb + 4H + Pb0 2 + 2S0 4 . 

The anions sulphuric acid and lead peroxide migrate to the 
positive pole and the cations lead and hydrogen to the nega- 
tive pole. However, on both the poles only those ions are 
separated for the precipitation of which the least work is 
required, or, in other words, whose decomposition-point is 
lowest, which in this case are lead peroxide and lead. Since, 
however, on account of the slight solubility and dissociation 
of lead salts, the ions in the immediate proximity of the elec- 
trodes would soon be exhausted, further charging can only 
take place when from the lead sulphate formed on the elec- 
trodes, fresh molecules are brought into solution, by the dis- 
sociation of which the precipitated ions are replaced, and 
charging is only finished when all the lead sulphate is dis- 
solved and separated as lead peroxide and lead-sponge. "With 
a further passage hydrogen-ions, which possess the next 



116 ELECTRO-DEPOSITION OF METALS. 

highest decomposition-point, are separated. The above-de- 
scribed process which in charging takes place by the action of 
the current, progresses in a reverse sense when, by connecting 
the positive and negative electrodes, the discharge is rendered 
possible, whereby the accumulator-current becomes available 
for exterior work. The lead peroxide is reduced and lead and 
lead sulphate are formed, while on the negative electrode the 
lead-sponge is oxidized, sulphate of lead being also formed at 
the same time. 

According to Liebenow's theory the electrolytic process is 
reversible without loss of energy, while, according to Elbs's, 
the process is irreversible and connected with a loss of energy. 
In most recent times, Dolezalek, Nernst, Loeb, and others, 
have expressed themselves in favor of Liebenow's view, while 
Le Blanc has discussed the possibility of the formation of lead 
peroxide-ions alongside of quadrivalent lead-ions. He as- 
sumes that at the moment of discharge, the latter are con- 
verted into bivalent lead-ions, the dissolving lead peroxide 
furnishing additional quadrivalent lead-ions, while at the 
moment of charging the bivalent lead-ions are converted into 
quadrivalent ones, and form lead peroxide. The view, that 
instead of one process in the accumulator, several processes 
are jointly enacted, may prove to be the correct one. 

Fig. 37 shows a common form of an accumulator. The 
separate electrodes are insulated from each other by glass 
tubes, the entire system being secured by lead springs which 
press the electrodes against the glass tubes. Small accumu- 
lator cells are of glass, hard rubber or celluloid, and larger 
ones of wood lined with lead. 

The sulphuric acid used for filling should be free from 
chlorine and metallic impurities, and have a specific gravity 
of 1.18. In a charged state of the accumulator, the specific 
gravity rises to about 1.21. 

Maintenance of accumulators. An accumulator should never 
be allowed to stand without being charged, since, in such a 
case, crystals of lead sulphate are formed upon the electrodes, 



SOURCES OF CURRENT. 



117 



which can only be removed with difficulty, and by this for- 
mation of crystals the accumulator acquires a very great re- 
sistance. When not in use an accumulator should be freshly 
charged every two weeks, because it gradually discharges itself. 
The acid should be put in the cells to such a height that 
the electrodes are covered about 5 millimeters deep and, since 
by the evaporation of water and, especially by the so-called 
"boiling" of the accumulator, i. e., by the escaping gases of 
oxygen and hydrogen, sulphuric acid is carried along, the ■ 
fluid has to be brought to its original level by the addition of 
dilute sulphuric acid of 1.05 specific gravity. 

Fig. 37. 




By the formation of lead peroxide and its subsequent reduc- 
tion, the positive electrodes readily undergo changes in vol- 
ume, they being liable to buckling and the scaling off of 
active mass ; lead-crystals of considerable length may deposit 
on % the negative electrodes, both these occurrences giving rise 
to short-circuiting. Hence, the accumulator should be fre- 
quently inspected, and the mass collecting on the bottom, as 
well as the lead-crystals, be removed. 

Charging of a cell should always be effected with a higher 



118 ELECTRO-DEPOSITION OF METALS. 

voltage than that of the cell, and the dynamo should only be 
coupled with the accumulator when it furnishes a current of 
sufficiently good electro-motive force. For a single cell, 
charging is commenced with an electro-motive force of 2 volts. 
Towards the completion of charging, the electro-motive force 
of the charging current should be 2.6 to 2.7 volts.. After 
interrupting the charging current the electro-motive force of 
each cell falls off to about 2.25 volts. 

During the discharge, the electro-motive force of the cells 
rapidly falls to about 2 volts each, remaining constant at this 
value for quite a long time, when it falls slowly to 1.8 volts, 
and rapidly from that point on. The appearance of the last- 
mentioned occurrence should by all means be avoided and, 
when the electro-motive force falls to 1.8 volts, discharge of 
current should be discontinued, as otherwise the electrodes 
would be subject to rapid destruction. 

Coupling accumulators. Like the voltaic cells, the individ- 
ual accumulators may, according to requirement, be coupled 
alongside one another (in parallel), or one after the other (in 
series). 

For the production of electrolytic depositions, cells of great 
capacity have to be taken exclusively into account, that is, 
cells capable of yielding a great strength of current for a cer- 
tain number of hours. This value, current-strength X time, 
is called ampere-hours capacity. 

If for an electrolytic process a maximum electro-motive 
force of 1.8 volts is required, one cell may be coupled to the 
bath, or if its capacity be insufficient, several such cells in 
parallel. If, on the other hand, the bath requires a greater 
electro-motive force, two or three cells will have to be coupled 
one after the other, and an excess of electro-motive force has 
to be destroyed by a resistance. The cells may be charged 
and discharged in parallel, or they may be discharged in 
series by means of a transformer, and vice versa, they may be 
charged in series and discharged in parallel, further details of 
which will be given in the Practical Part. 



« 



IV. 
PRACTICAL PART. 



CHAPTER IV. 

ARRANGEMENT OF ELECTRO-PLATING ESTABLISHMENT IN 

GENERAL. 

Although rules valid for all cases cannot be given, be- 
cause modifications will be necessary according to the size and 
extent of the establishment, the nature of the articles to be 
electro-plated, and the method of the process itself, there are, 
nevertheless, certain main features which must be taken into 
consideration in arranging every establishment, be it large or 
small. 

Light in plating rooms. Only rooms with sufficient light 
should be used, since the eye of the operator is severely taxed 
in judging whether the articles have been thoroughly freed 
from fat, in recognizing the different tones of color, etc. A 
northern exposure is especially suitable, since otherwise the 
reflection caused by the rays of the sun may exert a disturbing 
influence. For larger establishments the room containing the 
baths should, in addition to side-lights, be provided with a 
sky-light, which, according to the location, is to be protected 
by curtains from the rays of the sun. 

Ventilation. Due consideration must be given to the fre- 
quent renewal of the air in the rooms. Often it cannot be 
avoided that the operations of pickling, etc., must be carried 
on in the same room in which the baths are located. Espe- 
cially unfavorable in this respect are smaller establishments 
working with batteries, in which the vapors evolved from the 

(119) 



120 ELECTRO-DEPOSITION OF METALS. 

latter are added to the other vapors, and render the atmos- 
phere injurious to health. Hence, if possible, rooms should 
be selected having windows on both sides, so that by opening 
them the air can at any time be renewed, or the baths and 
batteries should be placed in rooms provided with chimneys. 
By cutting holes of sufficient size in the chimneys near the 
ceilings of the rooms, the discharge of injurious vapors will in 
most cases be satisfactorily effected. 

To those working with Bunsen cells, it is recommended to 
place them in a closet varnished with asphalt or ebonite lac- 
quer, and provided with lock and key. The upper portion 
of the closet should communicate by means of a tight wooden 
flue with a chimney or the open air. 

Heating the plating rooms. Since the baths work with 
greater difficulty, more slowly and more irregularly below a 
certain temperature, provision for the sufficient heating of the 
plating rooms must be made. Except baths for hot gilding, 
platinizing, etc., the average temperature of the plating solu- 
tions should be from 64.5° to 68° F., at which they work best; 
it should never be below 59° F., for reasons to be explained 
later on. Hence, for large operating rooms such heating 
arrangements must be made that the temperature of the baths 
cannot fall below the minimum even during the night, other- 
wise provision for the ready restoration of the normal temper- 
ature at the commencement of the work in the morning has to 
be made. Rooms heated during the day with waste steam from 
the engine, generally so keep the baths during the winter — the 
only season of the year under consideration — that they show in 
the evening a temperature of 64.5° to 68° F., and if the room 
is not too much exposed, the temperature, especially of large 
baths, will only in rare cases fall below 59° F. For greater 
security the heating pipes may be placed in the vicinity of the 
baths, but if this should not suffice to protect the baths from 
cooling off too much, it is advisable to locate in the plating 
room a steam conduit of small cross-section fed from the boiler 
and to pass steam for a few minutes through a coil of a metal 



ELECTRO-PLATING ESTABLISHMENTS. 121 

indifferent to the plating solution suspended in the bath. In 
this manner baths of 1000 quarts, which on account of several 
days' interruption in the operation, had cooled to 36° F., were 
in 10 minutes heated to 68° F. 

It has also been tried to heat large baths, for instance, nickel 
baths, by electrically heated boilers. The consumption of 
current is, however, very great, and the boilers- of nickel sheet 
thus far do not answer all rational demands, especially as re- 
gards durability. 

For smaller baths it is advisable to bring a small portion of 
them in a suitable vessel to the boiling-point over a gas flame, 
and add it to the cold bath. If, after mixing, the tempera- 
ture is still too low, repeat the operation. 

Renewal of water. Another important factor for the rooms 
is the convenient renewal of the waters required for rinsing 
and cleansing. Without water the electro-deposition of metals 
is impossible ; the success of the process depending in the first 
place on the careful cleansing of the metallic articles to be 
electro-plated, and for that purpose water, nay, much water, 
hot and cold, is required, as will be seen in the section treating 
on the " Preparation of the Articles." Large establishments 
should, therefore, be provided with pipes for the admission 
and discharge of water, one conduit terminating as a rose over 
the table where the articles are freed from grease. In smaller 
establishments, where the introduction of a system of water- 
pipes would be too expensive, provision must be made for the 
frequent renewal of the cleansing water in the various vats. 

Floors of the plating rooms. In consequence of rinsing, and 
transporting the wet articles to the baths much moisture col- 
lects upon the floors of the plating rooms. The best material 
for floors of large rooms is asphalt, it being, when moist, less 
slippery than cement. A pavement of brick or mosaic laid in 
cement is also suitable, but has the disadvantage of cooling 
very much. The pavement of asphalt or cement should have 
a slight inclination, a collecting basin being located at the 
lowest point, which also serves for the reception of the rinsing 



122 ELECTRO-DEPOSITION OF METALS. 

water. Wood floors cannot be recommended, at least for large 
establishments, since the constant moisture causes the wood 
to rot. However, where their use cannot be avoided, the 
places where water is most likely to collect should be strewn 
with sand or sawdust, frequently renewed, or the articles 
w r hen taken from the rinsing water or bath be conveyed to the 
next operation in small wooden buckets or other suitable 
vessels. 

Size of plating room. The plating room should be of such a 
size as to permit the convenient execution of the necessary 
manipulations. Of course, no general rule can be laid down 
in this respect, as the size of the room required depends on 
the number of the processes to be executed in it, the size and 
number of articles to be electroplated daily or within a certain 
time, etc. However, there must be sufficient room for the 
batteries or dynamo, for the various baths, between which 
there should be a passageway at least twenty inches wide, for 
•the table where the articles are freed from grease, for the lye 
kettle, hot-water reservoir, sawdust receptacle, tables for tying 
the articles to hooks, etc. 

Grinding and polishing rooms. The rooms used for grinding, 
polishing, etc., also require a good light in order to enable the 
grinder to see whether the article is ground perfectly clean, 
and all the scratches from the first grinding are removed. 
Where iron or other hard metals are ground with emery it is 
advisable to do the polishing in a room separated from the 
grinding shop by a close board partition ; because in the pre- 
paratory grinding with emery, which is done dry, without the 
use of oil or tallow, the air is impregnated with fine particles of 
emery, which settle upon the polishing wheels and materials, 
and in polishing soft metals cause fine scratches and fissures 
which spoil the appearance of the articles, and can be removed 
only with difficulty by polishing. Hence, all operations requir- 
ing the use of emery, or coarse grinding powders, should be 
performed in the actual grinding room, as well as the grinding 
upon stones and scratch-brushing by means of rapidly revolv- 



ELECTRO-PLATING ESTABLISHMENTS. 123 

ing steel scratch-brushes. Articles already plated are, of 
course, scratch-brushed in the plating room itself, either on the 
table used for freeing the articles from grease, or on a bench 
especially provided for the purpose. In the polishing room 
are only placed the actual polishing machines, which by means 
of rapidly revolving wheels of felt, flannel, etc., and the use of 
polishing powders, or polishing compositions, impart to the 
articles the final luster before and after electro-plating. The 
formation of dust in the polishing rooms is generally overesti- 
mated ; it is, however, sufficiently serious to render necessary 
the separation by a close partition of the polishing rooms from 
the electro-plating room, otherwise 'the polishing dust might 
settle upon the baths and give rise to various disturbing phe- 
nomena. In rooms in which large surfaces are polished with 
Vienna lime, as, for instance, nickeled sheets, the dust often 
seriously affects the health of the polishers, especially in badly 
ventilated rooms, and in such cases it is advisable to provide 
& suitable apparatus for keeping the dust out of the room. If 
this cannot be done, wooden frames covered with packing- 
oloth, placed opposite the polishing lathes, render good ser- 
vice; the packing-cloth by being frequently moistened with 
water retains a large portion of the dust. 

Many of the states now have laws compelling firms to install 
some kind of apparatus to keep the dust out of the room. 
There are many schemes of installing these exhaust fans, the 
most common of which is, according to T. C. Eichstaedt,* as 
follows: A fan or blower of sufficient capacity for the number 
of lathes in use is generally placed at one end of the room, 
driven by a belt or directly connected with a motor. The 
latter is the most economical and the better of the two. Then 
the polishing and buffing lathes are placed in a straight line 
and a large galvanized iron pipe, having openings with intake 
pipes and hoods for each wheel, is run to the floor behind each 
lathe. 

* Metal Industry, March, 1913. 



124 ELECTRO-DEPOSITION OF METALS. 

Distance between machines. Care should be taken to have 
sufficient room between the separate machines to prevent the 
grinders and polishers, when manipulating larger pieces of 
metal, from inconveniencing each other. Tables for putting 
down the articles should also be provided. 

Transmission. For grinding lathes requiring the belt to be 
thrown off in order to change the grinding, it is best to place 
the transmission carrying the belt pulleys at a distance of 
about three feet from the floor, while for lathes with spindles 
outside the bearings the transmission may be on the ceiling or 
wall. The revolving direction of the principal transmission 
should be such as to render the crossing of the belts to the 
grinding and polishing machines unnecessary, otherwise the 
belts on account of the great speed will rapidly wear out. 

The more modern electricalty-driven grinding and polish- 
ing machines are briefly called grinding and polishing motors, 
and have decided advantages over machines driven by belts. 
They will be referred to later on in the section " Mechanical 
Treatment." 

Electro-plating Arrangements in Particular. 

The actual electro-plating plant consists of the following 
parts : 1. The sources of current (batteries or d} 7 namo-electric 
machines) with auxiliary apparatus. 2. The current-conductors. 

3. The baths, consisting of the vats, the plating solutions, the 
anodes, and the conducting rods with their binding-screws. 

4. The apparatus for cleansing, rinsing, and drying. 

Before entering into the discussion of these separate parts of 
an electro-plating plant, it will first be necessary to speak of 
the electric conditions in the electrolyte, since what will here 
be said applies to all electro-plating processes, and will serve 
for a better comprehension of the succeeding sections. 

Current- density. For the result of the electrolytic process, 
the requisite to be taken first of all into consideration is, that a 
sufficient quantity of current acts upon the surfaces of the ob- 
jects to be electro-plated, and next that the current possesses 



ELECTRO-PLATING ESTABLISHMENTS. 125 

sufficent electro-motive force for the decomposition of the 
bath. The quantity of current which is necessary for the nor- 
mal formation of an electro-deposit upon 1 square decimeter 
= 10 x 10 centimeters (100 square centimeters) is now desig- 
nated as the current-density. In the electro-plating processes 
to be described later on, the suitable current-density is always 
given. If, for instance, this normal current-density is for a 
nickel bath, 0.4 ampere per square decimeter, the electro- 
motive force 2.5 volts, and the largest object-surface to be 
nickeled in the bath, 50 cm. x 20 cm. = 1000 square centi- 
meters, a current strength of at least 0.4 x 10 = 4 amperes is 
required. A Bunsen cell, which furnishes 4 amperes, would 
therefore suffice if the electro-motive force required for the de- 
composition of the electrolyte did not amount to 2.5 volts. 
As previously mentioned, a Bunsen cell furnishes about 1.8 
volts, and to attain the greater electro-motive force two cells 
have to be coupled one after the other. The performance of 
the battery would then amount to 4 amperes and 3.6 volts, 
and the excess of electro-motive force, which would be an im- 
pediment to deposition proceeding in a normal manner, has 
to be destroyed by a current-regulator to be described later on, 
in case it is not preferred to increase the object-surface in the 
bath. 

For silvering the current-density amounts to 0.25, and a 
silver bath with a slight excess of potassium cyanide requires 
1 volt. If now, for instance, an object-surface of 55 square 
decimeters, about equal to 50 large soup spoons, is to be 
silvered, 55 x 0.25 = 13.75 amperes and 1 volt are required. 
Hence three cells of 5 amperes each have to be coupled along- 
side each other to obtain 15-amperes current-quantity. 

The abbreviation of ND 100 is used to designate the normal 
current-density. By multiplying it with the number of square 
decimeters which the object-surface represents, the current- 
strength required for the object-surface is found. 

When the current-density with which deposition is made is 
known, the quantity by weight of the deposit effected in a 



126 ELECTRO-DEPOSITION OF METALS. 

definite time can be readily calculated. The electro-chemical 
equivalent has been referred to on p. 60, and it has been 
established that it represents the number of coulombs which 
separates 1 gramme-equivalent of metal per second. When 
by 1 coulomb, i. e., by 1 ampere, 0.3290 mg. copper per second 
is separated from cupric oxide salts, 1.184 gr. copper' are 
separated in. the ampere-hour (3600 seconds). 

For practical purposes the quantities of a metal separated 
in 1 ampere-hour are designated as the electro-chemical equiv- 
alent of the ampere-hour, and the quantities of metal separated 
with a known current-strength in a definite time are obtained 
by multiplying the electro-chemical equivalent with the cur- 
rent-strength in amperes and the number of hours. 

For calculating the time in which with a known current- 
strength, a certain quantity by weight is obtained, the latter is 
simply divided by the weight of the ampere-hours deposit X 
the current-strength. 

Another problem may be to calculate the current-strength 
which is required for furnishing in a certain time a definite 
quantity by weight of deposit. For this purpose, divide the 
quantity by weight by the product of ampere-hours deposit 
and number of hours. 

We .will first of all illustrate these calculations by two ex- 
amples without regard to the current-output. Suppose the 
time is to be determined during which a square decimeter of 
surface has to remain in the nickel bath in order to acquire a 
deposit of -iV millimeter thickness with a current-density of 
0.4 ampere. First calculate the weight of the deposit by mul- 
tiplying the surface in square millimeters with the thickness 
and specific gravity. One square decimeter is equal to 10,000 
square millimeters, which, multiplied by T V millimeter, gives 
as a product 1000, which multiplied by the specific gravity 
of nickel — 8.6 — gives 8600 milligrammes = 8.6 grammes. 
Hence a deposit of -fV milligramme thickness upon a surface 
of 1 square decimeter represents a weight of 8.6 grammes. 
Since, for the normal deposit per square decimeter, a current- 



ELECTRO-PLATING ESTABLISHMENTS. 127 

density of 0.4 ampere is required, and 1 ampere deposits, ac- 
cording to the table given on p. 61, ] .1094 grammes in 1 hour, 
\ ampere deposits 0.4437 gramme in 1 hour, and, therefore, 
about 19f hours will be required for the deposition of 8.6 
grammes. 

For calculating the time which one, two or more dozen of 
knives and forks or spoons, which are to have a deposit of 
silver of a determined weight, must remain in the bath when 
the current-density is known, proceed as follows : Suppose 50 
grammes of silver are to be deposited upon 1 dozen of spoons, 
and the most suitable current-density is 0.2 ampere per square 
decimeter; if the surface of 1 spoon represents 1.10 square 
decimeters, the surface of 1 dozen spoons of equal size is 13.2 
square decimeters. Hence, they require 13.2 X 0.2 = 2.64 
amperes ; now, since \ ampere deposits in 1 hour 4.025 
grammes of silver, 2.64 amperes deposit in the same time 
10.62 grammes of silver, and with this current, the dozen 
spoons must remain about 4f hours in the bath for the deposi- 
tion of 50 grammes of silver upon this surface. 

However, the figures obtained are correct or approximately 
correct only when the current-output amounts to 100 per 
cent., or to approximately this value, as in the case with acid 
copper baths, silver, gold, zinc and tin baths ; with a smaller 
current-output as yielded by potassium cyanide copper and 
brass baths, and nickel baths, a suitable Correction has to be 
made. 

The current-output of a bath is best determined as follows : 
Deposit upon an accurately weighed plate (sheet) of metal for 
several hours with the normal current-density, and note the 
exact time of deposition and the quantity of current measured 
by a voltmeter inserted in the circuit. Rinse the plate first 
with water and then with alcohol and Ether, and dry thor- 
oughly. Weigh it and by deducting the previous weight, the 
weight of the deposit is found. Now calculate from the table 
of electro-chemical equivalents (p. 61) how much metal should 
have been precipitated in the time consumed by the current- 



128 ELECTRO-DEPOSITION OF METALS. 

strength used ; the result will be the theoretical current-output. 
The practical current-output in per cent, is found by multi- 
plying the weight of the deposit found by 100 and dividing 
by the calculated weight of the theoretical current-output. 

Suppose the plate weighs 12.00 grammes and after having 
deposited upon it nickel for 3 hours with 1.5 ampere, it 
weighs 16,45 grammes, which corresponds to a deposit of 
nickel of 16.45 — 12.00 = 4.45 grammes. Theoretically, 
1.5 ampere should separate in 3 hours (1.1094 X 1.5 X 3) 
4.923 grammes of nickel. Hence, the practical current-output 
attained is 

4.925 : 4.45 = 100 : x 
x = 90.35 per cent. 

In calculating the quantity by weight, the product obtained 
from electro-chemical equivalent X current-strength X num- 
ber of hours, would have to be multiplied by the fraction 
■ Current-output in per cent . calculati the time the re _ 

100 S 

suit obtained above would have to be multiplied by the fraction 

_ , and for calculating the current- 

<;urrent-output in per cent. 

strength the quotient is likewise to be multiplied by the frac- 

100 

;tion : 

current-output in per cent. 

Electro-motive force in the bath. It has previously been seen 
that for the permanent decomposition of an electrolyte, an 
•electromotive force is required which must be large enough 
to overcome the resistance of the electrolyte, as well as the 
polarization-current flowing counter to the main current. 

The resistance of the electrolyte is found by multiplying its 
specific resistance, i. e., the resistance of a fluid cube of 1 deci- 
meter side-length by the electrode distance in decimeters, and 
dividing by the object-surface expressed in square decimeters, 
thus, 

■n . \ ,,, , , i . Specific resistance X dm. electrode-distance 

Resistance of the electrolyte = -£ — 

dm. object-surface. 



ELECTRO-PLATING ESTABLISHMENTS. 129 

According to p. 21, the electro-motive force required for 
sending a certain current-strength through a conductor is 
equal to the product of current-strength and resistance. To 
■calculate this electro-motive force, the resistance of the electro- 
lyte, i. e., of the bath, as found above, has to be multiplied by 
the current-density. 

For the better understanding, an example may here be 
given, the problem being to copper in an acid copper-bath an 
object-surface of 100 square decimeters. 

Let the specific resistance of the acid copper-bath of a given 
composition be 0.92 ohm, the electrode-distance 1.2 decimeters, 
the normal current-density 1.25 amperes. The required cur- 
rent-strength, J, is found by multiplying the normal density 
by the object-surface in square decimeters, thus, 

J = 100 X 1.25 = 125 amperes. 

From what has above been said, the resistance, W, of the 
•electrolyte is obtained by multiplying the specific resistance 
by the electrode-distance in decimeters, and dividing the 
product by the object-surface in square decimeters : 

92 X 1 2 
W= - ' IQ0 ' = 0.01104 ohm. 

From this the electro-motive force, E, required to send the 
current-strength, J, through the bath is calculated : 

E = J X W = 125 X 0.01104 = 1.38 volt. 

However, this is valid only for the normal temperature of 
18° C. (64.40° F.). If the electro-motive force has to be 
calculated, which is required at a higher temperature, for 
sending the current-strength of 125 amperes through the bath, 
we have to fall back upon the temperature-coefficients and 
the formulas given' for them on p. 26, whereby, if the tem- 
perature of the bath is 24° C. (75.2° F.), the equation assumes 
the following form : 
9 



130 ELECTRO-DEPOSITION OF METALS. 

Specific resistance = 0.92 (1 — 0.0113 X 6) = 0.858 ohm. 

Hence the temperature-coefficient 0.0113 has to be multi- 
plied by the number of degrees C, the bath is warmer than 
18° C, the product subtracted from 1, and the remainder 
multiplied by the specific resistance at 18° C, 0.92 ohm. It 
will be seen that the specific resistance (Sp. R.), which amounts 
at 18° C. to 0.92 ohm, amounts at 24° C. only to 0.858 ohm. 
The resistance, W, of the electrolyte at 24° C. is therefore 

0.858 X 1.2 n _ nn [ 
W = jqq = 0.0103 ohm, 

and the electro-motive force, E, which is capable of forcing 
125 amperes through the resistance of 0.0103 ohm : 

E = J X W = 125 X 0.0103 = 1.287 volt. 

If the electrolyte is 6° C. colder than 18° C, the formula is 
so changed that the temperature-coefficient 0.0113 has to be 
multiplied by 6, the product added to 1, and the sum multi- 
plied by the specific resistance (Sp. R.) : 

Sp. R. = 0.92 (1 + 0.0113 X 6) = 0.9824 ohm ; 

the resistance of the bath is then : 

W^ - 982 ^ 12 = 0.01178 ohm, 

the electro-motive force required being therefore : 

E = J X W = 125 X 0.01178 = 1.472 volt. 

Electro-motive counterforce of polarization. In addition to 
this resistance of the electrolyte, the electro-motive counter- 
force of the polarization-current has to be taken into consider- 
ation. The causes of polarization have been explained on p. 
65 ; it being partly due to the formation of gas-cells during 



ELECTRO-PLATING ESTABLISHMENTS. 131 

electrolysis with insoluble electrodes, especially anodes, partly 
to changes in concentration in the vicinity of the electrodes, or 
to oxidizing or reducing processes in the electrolyte. In most 
cases of electrolysis coming here in question, the dilution 
formed on the cathodes by the separation of metal will send a 
polarization-current towards the more concentrated layers of 
fluid formed by the solution of the anode-metal, to which is 
added the counter-current formed by the contiguity Of fluids 
with salts of a lower degree of oxidation to fluids with salts of 
a higher degree of oxidation. ' The magnitude of polarization 
is materially influenced b}^ the nature of the metals of which 
the electrodes consist ; the more electro-positive the cathode- 
metal and the more electro-negative the anode-metal, the 
greater the electro-motive force of the polarization-current 
which flows from the more positive cathode to the negative 
anode, hence in an opposite direction to the main current, 
which enters at the anode and passes out at the cathode. 
This explains why in nickeling iron less electro-motive force is 
required than in nickeling zinc, iron being only to a slight 
degree more positive than the nickel-metal of the anode, and 
hence less electro-motive counterforce appears. Zinc, .on the 
other hand, is far more positive than iron, and the electro- 
motive force of the polarization-current is consequently essen- 
tially stronger. 

The determination of this electro-motive counterforce is in 
the most simple manner effected by experiment. If a volt- 
meter of great resistance be placed at the bath, and the main 
current which had been passed into the bath be suddenly in- 
terrupted by means of a switch, the needle of the voltmeter 
does not at once return to the O-point, but remains for some 
time in a position above that point, and then gradually re- 
turns to it. The electro-motive force indicated by the needle 
for the short time after the interruption of the current gives 
the electro-motive force of the polarization-current. 

The electro-motive counterforce is influenced by the magni- 
tude of the current-density, growing and falling with the latter. 



132 ELECTRO-DEPOSITION OF METALS. 

When the magnitude of the counterforce has been determined 
by experiment as above described, the electro-motive force of 
the main current required for the electrolytic process is made 
up of the electro-motive force found by multiplying the current- 
strength by the resistance of the electrolyte plus the electro- 
motive counterforce of polarization found b}' experiment. 

Proceeding from the opinion that the electric current-lines 
are subject to scattering similar to the magnetic lines of force, 
Pfanhauser has taken into account the magnitude of this scatter- 
ing of the current-lines for the calculation of the resistance of 
the electrolyte. When such scattering takes place, the current- 
lines will not collectively migrate by the shortest road from the 
anode to the cathode, but describe greater or smaller curves, 
the cross-section of the fluid which takes part in the conduc- 
tion of the current, becoming thereby greater than if the cur- 
rent would pass, without deviation whatever, between the elec- 
trodes, and the resistance of the electrolyte consequently be- 
comes smaller. The least scattering was found with electrodes 
of the same size, it increasing with the greater distance of the 
electrodes from each other. In electro-plating processes run- 
ning a normal course, the decrease in the resistance of the 
bath by the scattering of current-lines may practically be 
disregarded, and it will later on only be referred to in so far 
as various phenomena which appear in electro-plating have 
been explained by this scattering. 

We will now turn to the discussion of electro-plating installa- 
tions with the different sources of current, and the arrangement 
with cells will first be described. It will be necessary to specify- 
in this section all the laws and rules which are also valid for 
installations with other sources of current, and the reader is 
requested thoroughly to study this section, as repetition in 
subsequent sections is not feasible. 

A. Installations with Cells. 

Coupling of cells. Prior to the time when it became possible 
to calculate the normal current-strength for a definite object- 



ELECTRO-PLATING ESTABLISHMENTS. 133 

surface, because the magnitude to which the term current- 
density has been applied was not known, the transmission of the- 
quantity of current required for the electro-plating processes 
was effected in a purely empirical manner. The effective zinc 
surface of the cells was taken as the basis, and it was held that 
with baths of medium resistance a good deposit is generally- 
effected when the effective zinc-surface of the cells is of the 
same size as the object-surface which is to be plated, and as 
large as the anode-surfaces. The electro-motive force required 
was obtained by coupling a larger or smaller number of cells 
one after the other. Suppose we have a nickel bath which 
requires for its decomposition a current of 2.5 volts of electro- 
motive force. Now since, according to p. 78, a Bunsen cell 
devel6ps a current of 1.88 volts, the reduction of the nickel 
cannot be effected with one such cell alone, but two cells will 
have to be coupled for electro-motive force one after the other, 
whereby, leaving the conducting resistance of the wires out of 
consideration, an electro-motive force of 2 X 1.88 = 3.76 volts 
is obtained, with which the decomposition of the solution can 
be effected. 

If, on the other hand, we have a silver bath which requires 
only 1 volt for its decomposition, we do not couple two cells 
one after the other, because the electro-motive force of a single 
cell suffices for the reduction of the silver. On p. 88 it has 
been seen that by coupling the elements one after the other 
(coupling for electro-motive force) the electro-motive force of 
the battery is increased, but the quantity of current is not in- 
creased, and that to attain the latter, the cells must be coupled 
alongside of one another (coupled for quantity). Hence in a 
group of, for instance, three cells coupled one after another, 
only one single zinc surface of the cells can be considered 
effective in regard to the quantity of current. Now, the larger 
the area of articles at the same time suspended in the bath is, 
the greater the number of such effective zinc surfaces of the- 
group of cells to be brought into action must be ; and, if for 
baths with medium resistance, it may be laid down as a rule- 



134 



ELECTRO-DEPOSITION OF METALS. 



that the effective zinc surface must be at least as large as the 
surface of the articles, provided the surface of the anodes is at 
least equal to the latter, the approximate number of cells and 
their coupling for a bath can be readily found. 

Let us take the nickel bath of medium resistance which, as 
above mentioned, requires a current of 2.5 volts, and for the 
decomposition of which two cells must, therefore, be coupled 
one after the other, and suppose that the zinc surface of the 
Bunsen cells is 500 square centimeters, then the effective zinc 
surface of the two cells coupled one after the other will also be 
500 square centimeters ; hence a brass sheet 20 X 25 = 500 
centimeters can be conveniently nickeled on one side with 

Fig. 38. 




these two cells, or a sheet 10 X 25 = 250 centimeters on both 
sides. Now suppose the surface to be nickeled were twice as 
large, then the two cells would not suffice, and a second group 
of two cells, coupled one after the other, would have to be 
joined to the first group for quantity, as shown in Fig 19, or 
perspectively in Fig. 38. Three times the object-surface 
would require three groups of elements, and so on. 

In giving these illustrations it is supposed the objects are 
to have a thick, solid plating. For rapid plating and a thin 
deposit a different course has to be followed. Only a slight 
excess of electro-motive force in proportion to the resistance of 
the bath being in the above-mentioned case present, reduction 
takes place slowly and uniformly without violent evolution of 



ELECTRO-PLATING ESTABLISHMENTS. 135 

gas on the objects, and by the process thus conducted, the 
deposit formed is sure to be homogeneous and dense, since it 
absorbs but slight quantities of hydrogen, and in most cases it 
can be obtained of such thickness as to be thoroughly resistant. 

For rapid plating, without regard to great solidity and 
thickness of the deposit, the cells, however, have to be coupled 
so that the electro-motive force is large as compared with the 
resistance of the bath, so that the current can readily overcome 
the resistance. This is accomplished by coupling three, four, 
•or more cells one after the other, as shown in the scheme, Fig. 
18. However, special attention has to be drawn to the fact 
that deposits produced with a large excess of electro-motive 
force can neither be dense nor homogeneous, because, in 
accordance with the generally accepted view, the deposits con- 
dense and retain relatively large quantities of hydrogen gas, 
•the term occlusion being applied to this property. 

Current regulation. Only in very rare cases will it be possi- 
ble to always charge a bath or several baths with the same 
object-surface ; and according to the amount of business, or 
the preparation of the objects by grinding, polishing and 
pickling, at one time large, and at another, small surfaces will 
be suspended in the bath. Now, suppose, a battery suitable 
for a correct deposit upon a surface of, say five square feet, 
has been grouped together ; and, after taking the articles from 
the bath, a charge of objects only half as large as before is 
introduced, the current of the battery will, of course, be too 
strong for this reduced surface, and there will be danger of 
the deposit not being homogeneous and dense, but forming 
with a crystalline structure, the consequence of which, in most 
cases, will be slight adhesiveness, if not absolute uselessness. 
With sufficient attention the total spoiling of the articles 
might be prevented by removing the objects more quickly 
from the bath. But this is groping in the dark, the objects 
being either taken too soon from the bath, when not suffi- 
ciently plated, or too late, when the deposit already shows the 
consequences of too strong a current. 



136 



ELECTRO-DEPOSITION OF METALS. 



For the control of the current an instrument called a cur- 
rent-regulator, resistance board or rheostat has been devised, 
which allows of the current-strength of a battery being re- 
duced without the necessity of uncoupling cells. It is obvious 
that the current of a battery, if too strong, can be weakened 
by decreasing the number of cells forming the battery, and 
also by decreasing the surface of the anodes, because the ex- 
ternal resistance is thereby increased. This coupling and 
uncoupling of cells is, however, not only a time-consuming, 
but also a disagreeable, labor ; and it is best to use a resistance 



Fig. 39. 




Fig. 40. 



TetheBWsh. 




To the J3cff> 



board with which, by the turn of a lever, the desired end is 
attained. Figs. 39 and 40 show this instrument. 

Its action is based upon the following conditions : As previ- 
ously explained, the maximum performance of a battery takes 
place when the external resistance is equal to the internal re- 
sistance of the battery. By increasing the external resistance, 
the performance is decreased, and a current of less intensity 
will pass into the bath when resistances are placed in the 
circuit. The longer and thinner the conducting wire is, and 
the less conducting power it possesses, the greater will be the 
resistance which it opposes to the current. Hence, the resist- 



ELECTRO-PLATING ESTABLISHMENTS. 



137 



ance board consists of metallic spirals which lengthen the 
circuit, contract it by a smaller cross-section, and by the nature 
of the metallic wire, has a resistance-producing effect. For a 
slight reduction of the current, copper spirals of various cross- 
sections are taken, which are succeeded by brass spirals, and 
finally by German-silver spirals, whose resistance is eleven 
times greater than that of copper spirals of •the same length 
and cross-section. In Fig. 39 the conducting wire coming 
from the battery goes to the screw on the left side of the re- 
sistance board, which is connected by stout copper wire with 
the first contact-button on the left ; hence by placing the 
metallic lever upon the button furthest to the left, the current, 



Fig. 41. 



BATH 




'f\tavXfi.Ui\ 




BATTERY 



passes the lever without being reduced, and flows off through 
the conducting wire secured to the setting-screw of the lever. 
By placing the lever upon the next contact button to the right, 
two copper spirals are brought into the circuit ; by turning the 
lever to the next button, four spirals are brought into the 
circuit, and so on. By a proper choice of the cross-sections of 
the spirals, their length, and the metal of which they are 
made, the current may be more or less reduced as desired. 

In case great current-strengths must flow through the re- 
sistance board, it is more advantageous to couple the spirals 
in parallel, and not one after the other, as in Figs. 41 and 42. 



138 



ELECTRO-DEPOSITION OF METALS. 



The resistance boards may be placed in the circuit itself in 
two different ways. If the resistance board is to maintain the 
electro-motive force of the current at the bath constant at a 
certain height, it is coupled in series. In this case the same 
current-strength which is consumed at the bath flows through 
the resistance. This coupling in series, or one after the other, 
•of the resistance board is shown in Fig. 41. 

In the other mode of coupling, Fig. 42, the resistance lies 
in shunt to the circuit, it being coupled parallel to it. Accord- 
ing to Kirchoff's law, if there be a branching-off of the 
■current, the sum of the current-strengths in the separate 



Fig. 42. 



bat a 




Jii&vlWcK/ 




BATTERY 



branches is just as great as the current-strength prior to and 
after branching off, and the current-strengths in the separate 
branches are inversely proportional to the resistances of the 
separate branches. 

In the case in question the coupling of the resistance-board 
(Fig. 42) represents such a branching-oft of the current ; the 
greater the resistance of the resistance-board, the less the 
current-strength will be which flows through it ; otherwise, a 
greater resistance in the main circuit, hence in this case in the 
bath, will cause a portion of the current-strength to flow through 
the resistance-board, where it is destroyed. 



ELECTRO-PLATING ESTABLISHMENTS. 139 

The parallel coupling of the resistance-board with the bath 
is utilized to remove differences in the operating electro- 
motive force of baths coupled in series, which may appear 
by electrode-surfaces of uneven size, or by changes in the 
resistances of the electrolytes. 

Current indicator. In order to be able to control the change 
in the current-conditions which is effected in a circuit by the 
resistance-board, a galvanometer is coupled behind the latter. 
This instrument consists of a magnetic needle oscillating upon 
a pin, below which the current is conducted through a strip of 
copper, or, with weaker currents, through several coils of wire. 
The electric current deflects the magnetic needle from its north- 
pole position, and the more so the stronger the current is ; 
hence the current-strength of the battery can be determined 
by the greater or smaller deflection. 

For a weak current, such as, for instance, that yielded by 
two cells, it is of advantage to use a horizontal galvanometer 
(Fig. 43). It is screwed to a table by 
means of a few brass screws in such a FlG - 43 - 

position that the needle in the north posi- 
tion, which it occupies, points to 0° when 
no current passes through the instru- 
ment. Articles of iron and steel must, of 
course, be kept away from the instrument. 
For stronger currents it is better to combine a vertical galvano- 
meter with the switch-board and fasten it to the same frame, 
as shown in Fig. 44. The screw of the lever of the switch- 
board is connected with one end of the copper strip of the 
vertical galvanometer, while the other is connected with the 
screw on the right side of the switch-board, in which is se- 
cured the wire leading to the bath. The switch-board and 
galvanometer are placed in one conducting wire only, either 
in that of the anodes or of the objects, one of these wires 
being simply cut, and the end connected to the battery, is 
secured in the binding-screw on the side of the resistance 
board marked " strong," while the other end, which is in con- 




140 ELECTRO-DEPOSITION OF METALS. 

nection with the bath, is secured in the binding-screw on the 

Fig. 44. 




opposite side marked " weak." The entire arrangement will 
be perfectly understood from Figs. 44 and 45. 



Fig. 45. 




Fig. 46 shows the Hanson & Van Winkle Patent Under- 



ELECTRO-PLATING ESTABLISHMENTS. 141 

writer's Rheostat. It has twice the carrying capacity of any 
resistance board ever made for this purpose, it having sufficient 
length of wire to allow of turning down the highest electro- 
motive force used in plating, to the lowest figure called for, 
without showing heat or any unfavorable symptoms. By the 
use of this rheostat the output from a plating room using two 
or more tanks can be doubled, providing the dynamo has the 
current capacity. 

Fig. 46. 




Fig. 47 shows a special rheostat constructed by the Hanson 
& Van Winkle Co. for use on nickel, copper or brass solutions 
requiring heavy ampereage. For the reason that so large an 
ampere current is used the instrument is especially constructed 
to withstand any excessive heating to which it may be sub- 
jected. This rheostat may also be used in the main line to 
control the voltage of several tanks. It is suitable for solutions 
containing 175 to 200 square feet of nickel work, or on copper 
or brass baths of 100 to 125 square feet, or for zinc solution 
containing 75 feet of work surface. 

The advantages derived from the use of a resistance board 



142 



ELECTRO-DEPOSITION OF METALS. 



having been referred to, it remains to add a few words regard- 
ing the indications made by the galvanometer. Since the 
greater deflection of the needle depends, on the one hand, on 
the greater current-strength, and on the other, on the slighter 
resistance of the exterior closed circuit (conducting-wires, 
baths and anodes), it is evident that a bath with slighter re- 
sistance, when worked with the same battery and containing 

Fig. 47. 




the same surface of anodes and objects, will cause the needle 
to deflect more than a bath of greater resistance under other- 
wise equal conditions. 

Hence, the deductions drawn from the position of the needle 
for the electro-plating process are valid only for definite baths 
and definite equal conditions, but, with due consideration of 
these conditions, are of great value. 

Suppose a nickel bath to work always with the same surfaces 



ELECTRO-PLATING ESTABLISHMENTS. 143 

of objects and anodes, and experiments have shown that the 
suitable current-strength for this surface of objects is that at 
which the needle stands at 15° ; and suppose, further, that the 
battery has been freshly filled and causes the needle to deflect 
to 25°, then the lever of the resistance »board will have to be 
turned so far to the right that the needle in consequence of the 
interposed resistances returns to 15°. Now if, after working 
for some time, the battery yields a weaker current, the needle, 
by reason of the resistance remaining the same, will constantly 
retrograde, and has to be brought back to 15° by turning the 
lever to the left, when a current of equal strength to the former 
will again flow into the bath. This manipulation is repeated 
until finally the lever rests upon the button furthest to the left, 
at which position the current flows directly into the bath with- 
out being influenced by the resistances of the resistance board. 
If now the needle retrogrades below 15°, it is an indication to 
the operator that he must renew the filling of the battery if he 
does not prefer suspending fewer objects in the bath. For this 
reduced object-surface it is no longer required for the needle 
to stand at 15° in order to warrant a correct progress of the 
electric process, since the resistance being in this case greater, 
a deflection to 10°, or still less, may suffice. This example 
will make it sufficiently clear that the current-indication by 
the galvanometer is not and cannot be absolute, but that the 
deductions must always be drawn with due consideration to 
the conditions, namely, surfaces of objects and anodes, and 
distance between them. 

It frequently happens that, in consequence of defective con- 
tacts with the binding-screws of the battery, or by the con- 
ductors of the objects and of the anodes touching one another 
(short circuit with non-insulated conducting wires), no current 
whatever flows into the bath. Such an occurrence is immedi- 
ately indicated by the galvanometer, the needle being not at 
all deflected in the first case, while in the latter the deflection 
will be much greater than the usual one. 

The needle of the galvanometer also furnishes a means of 



144 ELECTRO-DEPOSITION OF METALS. 

recognizing the polarity of the current. If the galvanometer 
be placed in the positive (anode) conductor by securing the 
wire coming from the battery in the binding-screw on the 
south pole of the galvanometer, and the wire leading to the 
bath in the binding-screw on the north pole of the needle, the 
needle, according to Ampere's law, will be deflected in the 
direction of the hands of a watch, i. e., to the right if the ob- 
server stands so in front of the galvanometer as to look from 
the south pole towards the north pole, because the batten- 
current flows out from the positive pole through the conduct- 
ing wire, anodes, and fluid to the objects, and from these back 
through the object wire to the negative pole of the battery. If 
now in consequence of the counter-current formed in the bath 
by the metallic surfaces of dissimilar nature or other causes, and 
flowing in an opposite direction to that of the battery-current, 
the latter is weakened, the needle will constantly further retro- 
grade from the zero point, and when the counter- or polariza- 
tion-current becomes stronger than the battery-current, it will 
be deflected in an opposite direction as before. Hence, by 
observing the galvanometer, the operator can avoid the annoy- 
ing consequences of polarization, which will be further dis- 
cussed under nickeling. 

Measuring instruments. It may here be stated that the use 
of the galvanometer has been to a great extent abandoned, 
and measuring instruments are at present generally employed. 

For measuring the current-strength, the ampere-meter or 
ammeter is employed, and for measuring the electro-motive 
force of the current, the volt-meter, these instruments allowing 
of the direct reading off of the current-strength in amperes 
and of the electro-motive force in volts. 

Space will not permit us to enter into the different construc- 
tions of these measuring instruments, and only the principle 
of their construction will here in a few words be explained. 

It has previously been seen that with a given object- and 
anode-surface, the deposit in the plating bath depends chiefly 
on the current-strength and electro-motive force of the cur- 



ELECTRO-PLATING ESTABLISHMENTS. 145 

rent. The deposit will turn out most beautiful and most 
homogeneous only with a definite current-strength, and though 
the skilled operator may succeed by empirical experiments in 
obtaining a beautiful deposit without a knowledge of the cur- 
rent-conditions, this mode of working requires far more atten- 
tion than when by simply reading off the deflection of the 
needle on the measuring instruments, it can be ascertained 
that the bath works in the most rational manner, without 
having first to inspect the objects and the bath itself. Such 
instruments are a great convenience, especially with a varying 
size of the object-surface, particularly if each bath is provided 
with one, because the electro-motive force at the bath changes 
every time the object-surface is changed. Hence, as pre- 
viously stated, the current has every time to be regulated 
before it is allowed to pass into the bath, if the deposit is to 
be always of the same quality. 

While voltmeters allow of a reliable control of the electro- 
motive force in the bath, ammeters serve the purpose of recog- 
nizing, on the one hand, whether the current-strength required 
for a certain object-surface passes into the bath, if the calcu- 
lation of the total current-strength is based upon the normal 
current-density. On the other hand, they allow of the deter- 
mination of the quantities by weight of metal deposited, the 
weight of the deposit depending solely on the current-strength. 
Although it is not always necessary to know this, yet it is 
frequently desirable . to ascertain how great the current- 
strength is, in order to determine what demands are made on 
the battery or the dynamo. 

Notwithstanding their extraordinary simplicity, the instru- 
ments constructed according to Hummel's patent, are very 
sensitive, and do not change in the course of time as is the 
case with many other constructions. Their mode of action is 
based upon the phenomenon that soft iron is attracted by a 
current-conductor. In the scheme, Fig. 48, S is a circular 
current-conductor, consisting of a greater or smaller number 
of copper-wire coils. In the interior is a piece of thin sheet- 
10 



146 



ELECTRO-DEPOSITION OF METALS. 



Fig. 48. 



iron, E, connected with an axis of revolution, a. G is a 

weight which is to be lifted by the attractive force of the cur- 
rent S upon the 'iron E. The 
stronger the current, the greater 
the attraction of the coils lying 
next to the sheet-iron, and, hence, 
the greater the elevation of the 
weight, G, will be, and the further 
the indicator, Z, connected with 
the axis of revolution, and below 
which a scale is fixed, will deflect. 
As regards construction, the 
voltmeter and ammeter are alike 
with the exception of the coil S. 
In the voltmeter it consists of 
many windings of thin copper 
wire, and in the ammeter of but 
a few windings of stout copper 

wire, or in instruments for great current-strength, of a massive 

bent piece of copper. 

Fig. 49 shows the " Waverly " voltmeter, manufactured by 




Fig. 49. 




the Hanson and Van Winkle Co., Newark, N. J. It is in- 
tended for direct current circuits only; to 10 volts. It is 
furnished with binding posts for fourteen tanks, thus enabling 



ELECTROPLATING ESTABLISHMENTS. 



147 



the operator to use only one instrument in obtaining the read- 
ing of any number of tanks up to fourteen, by simply moving 
the switch lever to the tank numbers indicated on the switch 
of the instrument, and when used in connection with the 
patent tank rheostat, will enable the operator to reproduce at 
all times the same electrical conditions which by observation 
and experience he has found necessary in order to obtain a 
satisfactory deposit of uniform thickness and color in the 
shortest possible time. 

Fig. 50 shows the Weston ammeter. The ammeter is 

Fig. 50. 




placed in one conductor only, either in that of the objects or 
-of the anode, and thus the whole of the current must pass 
through it. The voltmeter, however, is connected with both 
conductors. On the point where the electro-motive force is to 
be measured, one of the binding posts of the voltmeter is con- 
nected by means of a copper wire with the object-conductor, 
and the other, with the anode-conductor. 

Fig. 51 illustrates the arrangement of the switch-board and 
ammeter with a bath operated by means of a battery. 

Voltmeter switch. If many baths are in operation in an 
-electro-plating plant, it would be quite an expense to furnish 



148 



ELECTRO-DEPOSITION OF METALS. 



each bath with a special voltmeter. However, this is unneces- 
sary, one voltmeter being sufficient for three or four baths. In 
order to be able to read off conveniently on the voltmeter the 
electro-motive force passing into one of these baths, a switch is 



Fig. 51. 







required, the construction of which will be seen from Figs. 52 
and 53. 

Fig. 52 shows the coupling of the main object-wire ( — ) and 
of the main anode-wire (+), which will be referred to later on, 
together with the resistance boards R 1 and R 2 , the voltmeter 
V, switch U, and the two baths. In Fig. 53 the coupling is 
enlarged, and upon this illustration the following description 
is based : Suppose the main object-wire and anode-wire to be 
connected with the corresponding poles of a dynamo-machine 
or a battery, which for the sake of a clearer view is omitted in 
the illustration. The switch U consists of a brass lever, 
mounted with a brass foot,. upon a board. In the foot is a 



ELECTRO-PLATING ESTABLISHMENTS. 



149 



screw, with which is connected by a 0.039-inch thick copper 
wire one of the pole-screws of the voltmeter. The brass handle 
slides with spring pressure upon contact buttons connected by 
•copper wire with the binding-screws 1, 2, 3, 4, 5 (upon the 



FiCx 52. 




switch), which serve for the reception of the 0.039-inch thick 
insulated wires 1, 2, 3, 4, for measuring the electro-motive 
force, which branch off from the various tanks or resistance 
boards. The other pole-screw of the voltmeter is directly con- 



150 



ELECTRO-DEPOSITION OF METALS. 



nected with the main anode-wire. From the main object-wire,, 
a wire, whose cross-section depends on the strength of the 
working current, passes to the screw marked "strong" of the 
resistance board i^; the screw marked "weak" of the resist- 
ance board R x is connected by a wire of corresponding thick- 
ness with the object-wire of bath I, and at the same time with 
the binding-screw 1 of the switch. The resistance board R 2y 
of the bath II, is in the same manner connected with the main 
object-wire, the bath, and the binding-screw 2 of the switch ; 

Fig. 53. 




also the resistance boards R 3 and R± of the baths III and IV, 
which are not shown in the illustration. With the main 
anode-wire each bath is directly connected by conducting the 
current to an anode-rod of the bath by means of binding- 
screws and a stout copper wire, and establishing a metallic 
connection between this anode-rod and the next one. How- 
ever, instead of connecting both, the current may also be con- 
ducted from the main anode- wire to each anode- rod. 

In the illustration, the handle of the switch rests upon the 
second contact-button to the left, which is connected with the 



ELECTRO-PLATING ESTABLISHMENTS. 151 

binding-screw 2 of the switch. In the latter is secured the 
wire for measuring the electro-motive force which leads from 
the resistance board R 2 ; hence the voltmeter V will indicate 
the electro-motive force of the current at bath II. Suppose 
that bath II is full of objects and, with the position of the lever 
of the resistance board at " weak," as shown in the illustration, 
the voltmeter indicates 1.5 volts, while the most suitable 
electro-motive force for the bath is 2.5 volts, the handle of the 
switch is turned to the left until the needle of the voltmeter 
indicates the desired 2.5 volts. 

If the handle of the switch U be turned to the left so that it 
rests upon the contact-button 1, the measuring wire of bath II 
is thrown out, and the voltmeter indicates the electro-motive 
force in bath I ; if the lever rests upon contact-button 3, the 
electro-motive force in bath III is indicated, and so on. 

Dependence of the current-density on the electro-motive force. 
If a current of known strength be at the outset conducted 
through electrodes of a certain size into a bath of determined 
resistance, and the electrode-surfaces be then doubled, the- 
current-strength must also be doubled in order to maintain the 
same current-density as before. By increasing the electrode- 
surfaces to twice their size, the resistance of the bath is, how- 
ever, reduced one-half the value it amounted to with electrodes 
of half the size, the increased electrode-surfaces corresponding 
to a cross-section of the bath-fluid enlarged in the same pro- 
portion. 

Suppose the resistance of the bath with an electrode-surface 
of 1 square decimeter amounted to 2.4 ohms, and the current- 
strength, which in this case also represents the current-density, 
had been 0.4 ampere, an increase of the electrode-surface to 2 
square decimeters will require a current-strength of 0.8 ampere, 
in order to maintain a current-density of 0.4 ampere per square 
decimeter. The resistance of the bath then declines from 2.4 
ohms to 1.2 ohm. According to the laws of Ohm, the resist- 
ance of 2.4 ohms required an electro-motive force of current- 
strength X resistance, hence of 0.4 X 2.4 = 0.96 volt. After 



152 ELECTRO-DEPOSITION OF METALS. 

increasing the electrode-surfaces to 2 square decimeters and 
raising the current-strength to 0.8 ampere, the resistance de- 
clined to 1.2 ohm. The electro-motive force then amounts to, 
0.8 X 1.2 = 0.96 volt, hence to exactly the same as in the 
first case. 

From this it follows, that with an unaltered electrode- 
distance, the current-density remains unchanged with varying 
electrode-surfaces, if the electro-motive force at the bath be 
kept constant at the same height. 

It is also obvious that with an increasing electro-motive force 
a't the bath, the current-density must also increase, because, 
according to the law of Ohm, the current-strength is equal to 
the electro-motive force divided by the resistance. Since the 
latter is not changed when the electrode-distance remains the 
same, the quotient will be adequately larger if the divisor 
remains the same and the dividend be increased. Hence the 
current-density becomes greater. 

Now, as for the production of a useful deposit, a certain 
current-density should not be exceeded, the voltmeter furnishes 
us the means to insure against failure by keeping the electro- 
motive force at the bath constant with a varying charge of t|ie 
latter, and such an instrument should not be wanting in an 
electro-plating establishment. 

Conductors. The most suitable material for conducting the 
current is chemically pure copper, its conducting power being 
next to that of silver, but the use of the latter noble metal for 
this purpose is of course excluded by reason of its costliness. 

The laws of Ohm have shown us that the current-strength 
depends on the magnitude of the electro-motive force and the 
resistance in the circuit ; the greater the resistance, the less the 
current-strength which can flow through the conductor. From 
this it follows that in order to reduce losses of electro-motive 
force to a minimum, conductors of adequate cross-sections 
should be selected. 

Conductors which cause a loss of more than 10 per cent, of 
the electro-motive force have to be considered insufficient as 



ELECTRO-PLATING ESTABLISHMENTS. 153 

regards dimensions, and it is recommended to entrust the 
installation of such, constructions only to competent hands 
-capable of making the calculations required for the purpose. 

In addition to the correct dimensions of the conductors, the 
mode of mounting them also deserves the greatest attention. 
All the connections of the conductors, which are called contacts, 
must be made in the most careful manner, since bad contacts 
•cause a transition-resistance, and, in such a case, a large 
decrease in electro-motive force could not be prevented even 
by conductors of ample dimensions. 

A distinction is made between main conductors and branch 
conductors, the former effecting the transmission of the current 
from the source of current to the baths, while the latter branch 
off from them to the separate baths. 

The positive main conductor or anode conductor is con- 
nected with the + pole of the source of current, and the nega- 
tive main conductor or object-conductor with the — pole. 

Both bare and insulated conductors are used. For con- 
ductors of larger cross-sections, bright electrolytic copper in 
the form of round bars or flat rails is employed, while for con- 
ductors of smaller cross-sections, copper wire covered with an 
insulating material, such as hemp or jute coated with asphalt 
or varnish suffices. For connecting certain movable parts 
with the rigid main conductor, flexible cables of copper wire, 
cither bare or insulated; are very convenient. 

Bare conductors must be fixed in such a manner that they 
do not touch each other, which would cause short-circuiting, 
and possibly danger of fire, nor come in contact with damp 
brick-work. This is effected by placing the conductors upon 
porcelain insulators, to which they are secured by wire. 

It is also advisable not to allow even thoroughly insulated 
conductors to lie directly one upon the other, as the insulation 
may happen to be damaged, and short-circuiting would result. 

As regards the dimensions of the conductors, it should, in 
view of the slight electro-motive force of the current used for 
electrolysis, be made a rule to calculate for every ampere cur- 



154 ELECTRO-DEPOSITION OF METALS. 

rent-strength one square millimeter of copper cross-section, it 
the entire circuit is not over 20 meters long. 

Connection of main conductors and branch conductors is- 
effected by inserting the ends of two round conductors in 
couplings, Fig. 54, securing them by means of screws, and 
filling any intermediate space with solder. If the round main 
conductors are to be run at an angle, the coupling, Fig. 55, is 
used, and the T-coupling, Fig. 56, is employed on the points 
from which branches are to be run at a right angle from the 
main conductor. 

Flat copper rails are connected in the most simple manner 
by means of a piece of copper-sheet and screws, the contact 
surfaces having been first tinned to prevent oxidation. 

Fig. 54. Fig. 55. Fig. 56. 




Tanks. The choice of material for the construction of tanks 
to hold the plating solutions depends on the nature and 
properties of the latter. 

Solutions containing potassium cyanide require tanks of 
stoneware, enameled cast-iron or impregnated wood. Welded 
steel tanks constructed by the oxy-acetylene welding process 
are also largely used for cyanide solutions, soap solutions, 
electric cleaners, etc. Nickel baths and other baths which do 
not attack pitch and wood may be kept in wooden tanks lined 
with pitch. The best material for wooden tanks without pitch 
lining is pitch-pine, it containing least tannic acid. Larch 
may also be used, but is inferior to pitch-pine. Wood which 
contains tannic acid spoils every nickel bath, causing dark 
nickeling, so that, for instance, an oak tank cannot be used. 
For smaller baths, up to 300 quarts, the most advantageous 
tank is one of stoneware or enameled iron. 



ELECTRO-PLATING ESTABLISHMENTS. 



155 



Wooden tanks must be carefully constructed, and should be 
securely clamped together with strong iron bars, riveted and 
bolted, as shown in Fig. 57. The tank is then coated with a 
mixture of equal parts of pitch and rosin boiled with a small 
quantity of linseed oil. Another mixture, which has been 
found to afford a good protective covering to wood, consists of 
10 parts of gutta-percha, 3 of pitch, and 1J each of stearine 
and linseed oil, melted together and incorporated. 

For large acid copper and nickel baths wooden tanks lined 
with chemically pure sheet-lead about 0.118-inch thick, and the 
seams soldered with pure lead, are quite suitable. Care must, 

Fig. 57. 




of course, be taken that neither the conducting rods nor the 
articles suspended in the bath and the anodes come in contact 
with the lead lining, and therefore the conducting rods should 
not be laid directly upon the tanks, but placed upon a few 
thick strips of dry wood. Further, the anodes should be 
suspended at a sufficient distance from the lead lining, be- 
cause with too small a distance, metal from the solution is 
precipitated upon the lead lining. The latter always becomes 
electric, which, however, does not matter, and if the anodes 
are at a greater distance from it than the objects no metal is 
precipitated upon it. If for the better exhaustion of the baths 
the anodes are suspended at a slight distance from the sides? 



156 ELECTRO-DEPOSITION OP METALS. 

•it is advisable to protect the lead lining with thin wooden 
■boards, or to insulate it by giving it two coats of asphalt- 
lacquer. However, for this purpose asphalt-lacquer prepared 
from the residues of the tar industry is not available, and a 
solution of Syrian asphalt, with a small quantity of Venice 
turpentine in benzine should be employed. 

Based upon careful investigations, such lead-lined tanks have 
been used for large copper and brass baths containing potassium 
cyanide without the slightest injury to the baths. If even a 
film of lead cyanide is formed upon the lead, it is insoluble in 
excess of potassium cyanide, and hence is entirely indifferent 
as regards the bath. However, for nickel baths containing 
large quantities of acetates, citrates and tartrates, these lead- 
lined tanks cannot be recommended, since these salts possess a 
certain power of dissolving lead oxide. However, the use of 
such baths has been almost entirely abandoned, and the small 
quantities of organic acid which occasionally serve for correct- 
ing the reaction of a nickel bath need not be taken into con- 
sideration. The lead lining might be dispensed with if it 
were not for the difficulty of keeping wooden tanks tight. 
Many plating solutions impair the swelling power of the wood, 
and with even a slight change in the temperature the tanks 
become pervious, the evil in time increasing. Tanks lined 
with lead, on the other hand, remain tight, and have the 
advantage that the baths can be boiled in them by means of 
steam introduced through a lead coil in the tanks. 

For large baths containing potassium cyanide, holders of 
brick laid in cement may also be used, or holders of boiler- 
plate lined with a layer of cement. For nickel baths cement- 
lined tanks cannot be recommended. If a tank of that kind 
is to be used, direct contact of the nickel solution with the 
cement lining should be prevented by applying to the latter 
at least two coats of asphalt-lacquer. Stoneware tanks do not 
•bear heating. 

When using lead steam coils or loops in plating tanks or 
those arranged for electric cleaning, the coil ends entering and . 




ELECTRO-PLATING ESTABLISHMENTS. 157 

returning from the solution should be connected to the heat- 
ing system with insulating joints, Fig. 58, 
in order to prevent leakage of the electric Fig. 58. 

current. 

Conducting fixtures. These include the 
conducting rods which serve for suspending 
the objects and anodes, and are laid across 
the tanks, as well as the binding-posts and 
screws and copper-connections used for con- 
necting the conducting rods. 

The cross-sections of the conducting rods are, on the one 
hand, dependent on the maximum current-strength which 
without greater resistance is to pass through them, and, on the 
other, on the weight of the objects and anodes to be suspended 
in the bath. The conducting rods may be drawn of hard cop- 
per, or for not considerable current-strengths may be made of 
brass or copper tubing with insertions of iron rods. Bi-metal, 
i. e., iron rods upon which has been deposited by electrolytic 
methods a coat of copper adequate to the current -strength, 
may be highly recommended. By reason of the intimate 
union of the copper with the iron, the latter takes part in the 
conduction, which is, as a rule, not the case with copper tubes 
with insertions of iron rods, in consequence of the formation 
of oxide and defective contacts. 

It is advantageous to provide the narrow sides of the tanks 
with semicircular notches for the conducting rods to rest in, to 
prevent their rolling away. When using stoneware tanks the 
conducting rods are laid directly upon the tanks. Tanks of 
other material must be provided with an insulated rim of 
wood, or the rods are insulated by pushing pieces of rubber 
tubing over their ends. According to the size of the bath, 
3, 5, 7, or more conducting rods, best of pure massive copper, 
or if this is too expensive, of strong brass tubing with iron 
rods inside, are used. 

The rods carrying the anodes, as well as those carrying the 
objects, must be well connected with each other. This is 



158 



ELECTRO-DEPOSITION OF METALS. 



effected by means of binding-posts and screws of the improved 
forms shown in Fig. 59, Nos. 1 and 2 being rod connections 
for tanks. No. 4, or double connection, is a very convenient 
form, as it can be adapted to so very many changes. The 



Fig. 59. 



No. 1. 



No. 3. 





No. 4. 



No. 2. 





three-way connection, No. 3, is so well known that it hardly 
needs an explanation. 

Arrangement of objects and anodes in the bath. To secure 
the uniform coating of the objects with metal they must be 
surrounded as much as possible by anodes, i. e., the positive- 



ELECTRO-PLATING ESTABLISHMENTS. 159 

pole plates of the metal which is to be deposited. For flat 
objects, it suffices to suspend them between two parallel rows 
of anodes, the most common arrangement being to place three 
rods across the bath, the two outermost of which carry the 
anodes, while the objects are secured to the center rod. For 
wide baths five conducting rods are frequently used, but they 
should always be so arranged that a row of objects is between 
two rows of anodes. The arrangement frequently seen with 
four rods across the baths, of which the outermost carry anodes, 
and the other two, objects, is irrational if the objects are to be 
uniformly plated on all sides, because the sides turned towards 
the anodes are coated more heavily than those suspended 
opposite to the other row of objects. 

For large round objects it is better to entirely surround 
them with anodes, if it be not preferred to turn them fre- 
quently, so that all sides and portions gradually feel the effect 
of the immediate vicinity of the anodes. (See "Nickeling.") 

For objects to be plated on one side only the center rod may 
be used for the anodes and the two outer ones for the objects; 
the surface to be plated being, of course, turned towards the 
anodes. 

There shonld be an ample supply Of anodes in the bath. 
In baths of base metals the anode-surface should at least be 
equal in size to the surface to be plated ; an exception being 
permissible in gold and silver baths. 

The anodes should not be too thin, because the thinner 
they are, the greater the resistance. Copper, brass and nickel 
anodes should not be less than 3 millimeters thick, and the 
hooks by which they are suspended should be correspondingly 
thick and numerous. 

The anodes are suspended from the cross-rods by strong 
hooks of the same metal, so that they can be entirely im- 
mersed in the bath (Fig. 60). Hooks of another soluble metal 
would contaminate the bath by dissolving in it, and this 
must be strictly avoided, as it would cause all sorts of 
■disturbances in the correct working of the bath. In case 



160 



ELECTRO-DEPOSITION OF METALS. 



Fig. 60. 



Fig. 61. 




hooks of another metal, except platinum, are used, the anodes 
must be suspended so that they project 
above the surface of the liquid, and the 
hooks not being immersed, are there- 
fore, not liable to corrosion ; but the 
anodes are then not completely used up, 
the portion dipping in the solution being 
gradually dissolved, whilst the portion 
projecting above the fluid remains intact. 
Instead of wire hooks, strips of the same 
metal as the anodes and fastened to them 
by a rivet may also be used (Fig. 61). 
For suspending the objects, lengths of 
soft, pure copper wire, technically called slinging wires, are 
used. They are simply suitable lengths of copper wire of a 
gauge to suit the work in hand, wire No. 20 Birmingham w r ire 
gauge being generally employed for such light work as 
spoons, forks and' table utensils. Wire of a larger diameter 
should be employed for large and heavy goods. The immersed 
ends of these wires becoming coated with the metal which is 
being deposited, they should be carefully set aside each time 
after use, and when the deposit gets thick it should be stripped 
off in stripping acid, and the wire afterwards annealed and 
straightened for future use. 

To keep the rods clean and to protect them from the fluid 
draining off from the articles when taken from the bath, it is 
advisable to cover them with a roof of strips of wood ( A)> or a 
semi-circular strip of zinc coated with ebonite lacquer ; by this 
means the frequent scouring of the rods, which otherwise is 
necessary in order to secure a good contact with the hooks of 
the anodes, is done away with. 

It need scarcely be mentioned that the anodes and the ob- 
jects to be plated must not touch each other, as short-circuiting 
would take place on the point of contact. 

The plating solutions, briefly called baths or electrolytes, 
will be especially discussed in speaking of the various electro- 



ELECTRO-PLATING ESTABLISHMENTS. 161 

plating processes. Other rules for suspending the objects will 
be mentioned under " Nickeling," and are valid for all other 
electro-plating processes. . 

Apparatus for cleansing and rinsing. It remains to consider 
the cleansing and rinsing contrivances, without which it would 
be impossible to carry on electro-plating operations. Every 
electro-plating establishment, no matter how small, requires at 
least one tub or vat in which the objects can be rubbed or 
brushed with a suitable agent in order to free them from 
grease. This is generally done by placing a small kettle or 
stoneware pot containing the cleansing material at the right- 
hand side of the operator alongside the vat or tub. Across 
the latter, which is half filled with water, is laid a board of 
soft wood covered with cloth, which ' serves as a rest for the 
objects previously tied to wires. The objects are then scrubbed 
with a brush, or rubbed with a piece of cloth dipped in the 
cleansing agent. The latter is then removed by rinsing the 
objects in the water in the tub and drawing them through 
water in another tub. By this cleansing process a thin film 
of oxide is formed upon the metals, which would be an im- 
pediment to the intimate union of the electro-deposit with the 
basis-metal. This film of oxide has to be removed by dipping 
or pickling, for which purpose another vat or tub containing 
the pickle, the composition of which varies according to the 
nature of the metal, has to be provided. After dipping, the 
objects have to be again thoroughly rinsed in water to free 
them from adhering pickle, so that for the preparatory cleans- 
ing processes three vessels with water, which has to be fre- 
quently renewed, as well as the necessary pots for pickling 
solutions, have to be provided. 

Larger plants require a special table for freeing the objects 
from grease. Such a table is shown in Fig. 62. It consists of a 
box furnished with legs, and is divided by four partitions into 
two larger and three smaller compartments. Boards covered 
with cloth are laid over the larger compartments, upon which 
the objects are brushed with lime-paste for the final thorough 
11 



162 



ELECTRO-DEPOSITION OF METALS. 



freeing from grease. Over each of these compartments is a 
rose provided with a cock, under which the objects are rinsed 
with water. The outlets for the waste water from the large 
compartments are in the bottom of the box and are provided 
with valves. Of the smaller compartments, the one in the 
center serves for the reception >of the lime-paste (see "Chemi- 
cal Treatment "), while the others contain each two pots or 
small stoneware tanks with pickling fluid. In Fig. 66 these 

Fig. 62. 




tanks are indicated by 11 and 12. The two marked 11 con- 
tain dilute sulphuric acid for pickling iron and steel articles, 
while those marked 12 contain dilute potassium c} 7 anide solu- 
tion for pickling copper and its alloys, and Britannia, etc. 
For cleansing smaller articles, four men can at one time work 
on such a table; but for cleansing larger articles only two. 
For an establishment which does not require such a large 
table, one with a larger and two smaller compartments may 
be used. The advantages of such a box-table are that every- 



ELECTRO-PLATING ESTABLISHMENTS. 



163 



thing is handy together ; that the pickle, in case a pot should 
break, cannot run over the floor of the workshop ; and that 
the latter is not ruined by pickle dropping from the objects. 
The small box on the side of the table serves for the reception 
of the various scratch-brushes. 

After having received the electro-deposit, the objects have 
to be again rinsed in cold water, which can be done in one of 
the three tanks or with the rose-jet, and finally have to be 
immersed in hot water until they have acquired the tempera- 
ture of the latter. How the water is heated makes no dif- 

Fig. 63. 




ference, and depends on the size of the establishment. The 
heated objects are then immediately dried in a box filled with 
•dry, fine sawdust that of boxwood, maple, or other wood free 
from tannin being suitable for the purpose. A steam sawdust 
box very suitable for the purpose is made in four removable 
sections, which consist of a smooth galvanized iron box, hot 
air chamber with asbestos lining closely built, f-inch steam 
radiator, and a rigid stand made of 1^-inch angle iron. 

To overcome various troubles and difficulties connected 



164 ELECTRO-DEPOSITION OF METALS. 

with drying by means of sawdust mixed with the articles: 
placed in the pan and heated, steam drying barrels have been 
introduced. One type is practically the same as the oblique 
tilting tumbling barrel in common use for cleaning metallic 
surfaces, except that it is jacketed and otherwise constructed 
to allow a circulation of steam about the inner barrel, auto- 
matic ejection of the condensation, still allowing the barrel to- 
be tilted. A barrel load can be thoroughly dried in a few 
minutes, especially if the work is shaken out of hot water. 
It will be readily understood that the rolling over and over 
of the hot barrel thoroughly mixes the work and sawdust, 
liberates the steam and precludes the possibility of water- 
marks, etc., and further, brightens the goods at the same time. 
A centrifugal dryer for small work, supplied by The Han- 
son & Van Winkle Co., N. J., is shown in Fig. 63. This 
machine should be used where mechanical plating apparatus 
is installed, one to three minutes only being necessary for 
drying small work. The machine is furnished with or with- 
out hoist, and is fitted with ball bearings. It can be supplied; 
with a tapered steel pan or a perforated straight-sided steel or 
copper basket for holding the work. 

B. Installations with Dynamo-Electric Machines. 

Setting up and running a dynamo. Most of the troubles 
with plating-dynamos are caused by neglecting one or more of 
the conditions necessary for their proper operation, and are 
not due to any defects in the machines themselves. The 
troubles most frequently encountered are, in order of their 
frequency, as follows : First, insufficient or variable speed. 
Second, improper setting of the brushes, and the use of im- 
proper lubricants and cleaning" material on the commutator. 
Third, poor oil, or an insufficient, or too great, an amount of 
oil in the bearings. Fourth, overloading the machine. 

It is important that the dynamo be properly placed, and the^ 
following considerations should govern the choice of location : 
The dynamo should not be exposed to moisture nor to the dirt. 



ELECTRO-PLATING ESTABLISHMENTS. 165 

and dust of the polishing room. Cleanliness is a necessity. 
A cool, well-ventilated room should be chosen. This is im- 
portant, for a well-ventilated machine will do more work with 
less wear on parts than one unfavorably placed. The machine 
should not be boxed in, as this will make it run hotter than it 
otherwise would. Not only this, the mere fact of having it 
totally boxed in precludes the probability of receiving the 
proper amount of attention. 

Except on the larger sizes of machines a special foundation 
is not mechanically necessary, providing the floor is fairly 
solid. On account, however, of dirt getting into the running 
parts when the floor is cleaned, it is always well to raise the 
machine from six to twelve inches above the floor. For a 
•small dynamo a well-made box of two-inch lumber will afford 
an ample foundation. For the larger sizes two or three strips 
•of 6-inch x 6-inch yellow pine may be used. In either case 
the box or strips should be solidly nailed or bolted to the floor 
and the machine secured to its base with four lag screws of 
the proper size. 

The direction of rotation may be ascertained by an inspec- 
tion of the brushes, the commutator running away from the 
brushes. One of the troubles mentioned above, namely, vari- 
able speed, may be remedied to a large extent by a suitable 
belt, run in the proper manner. The counter-shaft should 
never be run directly over the dynamo, but should be placed 
far enough to one side so that the belt will run diagonally and 
in such a direction that the under side of the belt does the 
work. This is on account of the fact that when the belt is 
running vertically or diagonally with the upper side doing 
the work it stretches and sags away from the pulley when a 
heavy load is thrown on the dynamo, thus giving less pull as 
the necessity for a greater pull increases. Use good, pliable, 
single belting with the hair side of the belt to the pulley on 
smaller and medium-size machines. For the larger sizes a 
thin, double belt may be used. 

After the machine has been properly set and belted, it re- 



166 ELECTRO-DEPOSITION OF METALS. 

mains to start it up. Before starting, remove the bearing caps 
and pour a small quantity of oil on the bearings ; loosen tbe- 
screw holding the rocker-arm in position, and be prepared to 
shift the rocker-arm backward or forward, so as to get tho 
brushes on the neutral or non-sparking line, as it often happens 
that the rocker-arm has been shifted from its proper position 
in transportation. 

The proper position for the tips of the brushes on all ma- 
chines of either the bipolar or multipolar type is about opposite 
the center of the poles. The tips of the brushes should also be 
spaced at even intervals, this being, on the two-pole machine, 
diametrically opposite to each other ; on the four-pole machine 
one-quarter of the circumference from each other ; on the six- 
pole machine, one-sixth of the circumference, and so on. The- 
exact position of the brushes (that is, where they run spark- 
lessly) can only be ascertained by trial. This adjustment should 
be made, in case it is necessary, as soon as the machine starts- 
up, for if it is allowed to run any length of time while sparking 
the commutator will be cut badly, and may necessitate taking 
out the armature and truing up the commutator. In case this 
is necessary, a sharp diamond-point tool should be used with a 
moderate speed, and the commutator should be finished with a 
fine second-cut file, and then with No. sandpaper and oil. 
After the proper adjustment of the brushes has been made, 
take an oil-can, and while the machine is running, pour oil 
slowly into the oil-well until the oil-rings take it up properly 
and carry it to the top of the bearings, where it enters the dis- 
tributing slot. If too little oil is in the well and the rings do 
not dip into it sufficiently deep, they will rattle around and 
spatter oil, whereas if too much oil is put in, it will run out at 
the ends of the bearings and get into the belt, winding and 
commutator of the machine. 

While the commutator should never be allowed to become 
greasy or dirty, it is equally important that it should not be 
run perfectly dry, so that the brushes cut. When it becomes 
dirty, after cleaning with No. sandpaper (emery should 



ELECTRO-PLATING ESTABLISHMENTS. 167 

never be used) it should be re-oiled by rubbing it with a 
woolen cloth moistened with kerosene oil, or with the very 
smallest amount of lubricating oil. The quality and kind of 
oil used for the bearings is important, and a regular dynamo 
oil should be used. Under no circumstances should vegetable 
or animal oil (such as castor or sperm oil) be used, but a light 
grade of mineral dynamo oil. 

The brushes should not only be properly set as regards their 
position around the commutator, but they should have careful 
individual setting. They should have a fair and even bedding 
on the commutator, and not touch on the heel or toe or on 
either edge, as the object is to get full contact surface between 
the brushes and the commutator. If the commutator is kept 
in proper shape and the brushes once properly set, it will not 
be necessary to adjust them often. As it is practically impos- 
sible to make a perfectly accurate setting of the brushes, and 
it takes them some few days to get worn down to a good con- 
tact, it will be seen that it does more harm than good to be 
continually re-setting them. If the ends of the brushes get 
very ragged, they should, in the case of wire-gauze brushes, 
be carefully trimmed with a pair of shears, and in the case of 
strip-copper brushes, filed with a fine second-cut file. The 
tension spring on the brush holder should be adjusted to make 
a light but positive contact, for if there is too much pressure, 
the brushes will cut the commutator, causing it to wear away 
rapidly. 

If there is any doubt about which is the positive and which 
is the negative pole of the dynamo, the polarity may be readily 
determined after starting up, by running two small wires from 
the dynamo and placing the ends in a glass of acidulated 
water. Around one of these wires more bubbles of gas will 
be thrown off than around the other, the one evolving the 
greater amount of gas being the negative pole, to which the 
work should be attached. 

Choice of a dynamo. For electrolytic processes, as previ- 
ously mentioned, shunt-wound and compound-wound dynamos 



168 ELECTRO-DEPOSITION OF METALS. 

are at present largely used. Their construction has already 
been explained, and there remains now only the question 
what size dynamo, i. e., of what capacity as regards current- 
strength and electro-motive force, is to be selected for a plant. 

We have learned that a certain object-surface requires a 
certain current-strength. Hence for plants with different 
baths, it is only necessary to fix the largest object-surface in 
square decimeters which is to be suspended in the separate 
baths and to multiply this number of square decimeters by 
the current-density in amperes, in order to find the supply of 
current required for each bath. The sum of the current re- 
quired for the separate bath, with an allowance of 20 to 25 
per cent, for an eventual enlargement, gives the current- 
strength the dynamo must furnish. It must of course be taken 
into consideration whether all the baths are to be in constant 
operation at the same time or not. In the latter case a smaller 
current-strength will of course suffice, and a smaller type of 
dynamo answer the purpose. 

The impressed electro-motive force of the dynamo should be 
such that, taking into consideration the decline of the electro- 
motive force in the conductors, it is, at the greatest current- 
capacity, about ^ to | volt greater than the highest electro- 
motive force of a bath required. 

For the purpose of explaining by an example the choice of 
a suitable dynamo, let us suppose that a nickel bath with an 
object surface of 50 sq. decimeters ; a potassium cyanide 
copper bath with an object surface of 30 sq. decimeters; a 
brass bath with an object surface of 40 sq. decimeters; a silver 
bath with an object surface of 10 sq. decimeters, are to be fed 
with current. 

The standard current-densities and electro-motive forces re- 
quired for the separate baths are given later on when speaking 
of them. It will there be found that the current-density for 
nickeling brass amounts to about 0.4 ampere, the electro- 
motive force being 2.5 volts ; for coppering, 0.35 ampere and 
3.0 to 3.5 volts are required ; for brassing also 0.35 ampere 



ELECTRO-PLATING ESTABLISHMENTS. 169 

•and 3.0 to 3.25 volts ; while for silvering 0.2 ampere and 1 
volt are on an average used. This amounts to 

For nickel bath 50 sq. decimeters X 0.4 ampere = 20 amperes. 
For copper bath 30 sq. decimeters X 0.35 ampere = 10.5 amperes. 
For brass bath 40 sq. decimeters X 0-35 ampere = 14 amperes. 
For silver bath 10 sq. decimeters X 0.2 ampere = 2 amperes; 



46.5 amperes. 



Hence 46.5 amperes are required for the simultaneous 
operation of these four baths, and a dynamo of 50 amperes 
current-strength and 4 volts impressed electro-motive force 
would have to be selected, since, taking into consideration, a 
permissible decline of electro-motive force of 10 per cent. = 
•0.4 volt in the conductors, there are still at disposal 3.6 volts, 
while the greatest electro-motive force required amounts to 
3.5 volts. 

Since the various baths of a larger establishment possess 
different resistances and cannot always be charged with the 
same object-surfaces, they have to be operated in parallel. 
This renders it necessary that for each separate bath working 
with a lower electro-motive force, the excess of electro-motive 
force as existing in the main conductor has to be destroyed by 
a resistance, called the main-current regulator or bath-current 
regulator. Hence as many main-current regulators must be 
provided as there are baths, and the regulators have to be 
•exactly calculated and constructed for the required effect. 
Thus in the above-mentioned example, the bath-current regu- 
lators, with an electro-motive force of 3.6 volts in the main 
conductor, must let pass for a nickel bath 20 amperes and 
destroy 1.1 volts ; let pass for a copper bath 10.5 amperes and 
destroy 0.6 to 0.35 volt ; let pass for a brass bath 14 amperes 
and destroy 0.6 to 0.35 volt ; let pass for a silver bath 2 amperes 
and destroy 2.6 volts. 

Since every destruction of electro-motive force means an 
economic loss, it follows that the impressed electro-motive force 
of the dynamo should not be greater than absolutely necessary, 



170 ELECTRO-DEPOSITION OF METALS. 

so that it can be reduced by a regulator to the lowest per- 
missible limit, and this limit should be constantly maintained. 
Thus, when the electrode surfaces in the bath are changed, 
and there is consequently also a change in the impressed 
electro-motive force, the latter can be properly adjusted by the 
regulator. If this were not done, and the impressed electro- 
motive force would become considerably greater, the bath- 
current regulators calculated for the destruction of a fixed 
electro-motive force would no longer be capable of fulfilling- 
their objects From what has been said, it will be seen that 
voltmeters are indispensable for electro-plating plants in order 
to be constantly informed as to the electro-motive force pre- 
vailing at the baths, and, if necessary, to correct it. 

By reason of the economic loss connected with the destruc- 
tion of an excess of electro-motive force, it may also have to 
be taken into consideration whether in larger plants it would 
not be better to use several dynamos with different impressed 
electro-motive forces than a single dynamo with an impressed 
electro-motive force required for the greatest electro-motive 
force for the baths. Suppose, for instance, there are present 
in a larger plant, in addition to nickel, brass and copper 
cyanide baths, which require a voltage of up to 3J volts, a 
large number of silver and tin baths and acid copper baths 
for galvanoplasty (with the exception of those for rapid gal- 
vanoplasty), for which an impressed electro-motive force of 2 
volts is quite sufficient, it would by all means be more judic- 
ious to use for the first-named baths a special dynamo with 
an impressed electro-motive force of 4 volts, and for the last- 
mentioned baths a dynamo with a voltage of 2 volts. 

Another question to be considered in the choice of a dynamo 
is, whether one or several accumulator cells are to be charged 
from it. This will be later on referred to. 

While, when baths are coupled in parallel, each bath receives 
its supply of current from the main conductor, and such parallel 
coupling is always required when baths of different nature, with 
unequal resistances and unequal electro surfaces, are con- 



ELECTKO-PLATING ESTABLISHM ENTS. 



171 



nected, baths requiring an equal, or approximately equal, 
current-strength may be coupled one after the other, i. e., in 
series. This principle of series-coupling of baths is illustrated 
by Fig. 64. 

The current passes through the anodes of the first bath into 
the electrolyte, flows through the latter and passes out through 
the object-wire. From there it goes through the anodes of the 
next bath to the objects contained in it, and so on, until it 
returns through the object-wire of the last bath to the source 
of current. 

Thus for series coupling of the baths, a dynamo with a. 

Fig. 64. 




greater impressed electro-motive force than the sum of the 
electro-motive forces of all the baths coupled one after the 
other has to be selected. On the other hand, baths coupled 
one after the other do not require a greater current-strength 
than a single bath. Suppose four baths, each charged with 
100 square decimeters of cathode- and anode-surfaces are 
coupled one after the other, and the electro-motive force of 
one bath amounts to 1.25 volts and the current-density to 2 
amperes. Then there will be required for one bath 100 X 2 
= 200 amperes and 1.25 volts, and for four baths coupled one 
after another, 200 amperes and 1.25 X 4 = 5 volts. 

The connection of the baths, resistance boards and measur- 
ing instruments to a shunt-wound dynamo is shown in Fig. 



172 ELECTRO-DEPOSITION OF METALS. 

65, and requires no further explanation. The resistance 
board at the right is the field resistance board, the other two 
belonging to the two baths which are coupled in parallel. 

Parallel coupling and series coupling of dynamo-machines. 
In establishing a larger electro-plating plant, the question 
may arise whether it would not be advisable to install two 
smaller dynamos instead of a single larger one capable of fill- 
ing all demands, even at the busiest season. The installation 
of two dynamos allows of the business being carried on with- 
out serious interruption in case one of the machines requires 
repairing, and in dull times one dynamo would, as a rule, be 
sufficient. In case two dynamos are installed, the main con- 
ductors must of course have the required cross-sections corre- 
sponding to the total current-strength of both machines. 

It, however, happens very frequently that as the plant be- 
comes larger by reason of an increase in the number of baths, 
a larger supply of current will in time be required. The 
question then arises whether to sell the old dynamo, which 
may be difficult, especially if it is of an obsolete pattern, or 
whether to supply the deficit of current by installing an ad- 
ditional dynamo. In such case, if the baths are not to be 
divided into groups, one of them being furnished with current 
from one dynamo and the other from the second machine, 
but both the dynamos are to be connected to a common main 
conductor, the cross-section of the latter must first of all be 
increased so as to be capable of carrying the total current- 
strength of both dynamos without material decrease in electro- 
motive force. Whether for this purpose a new conductor of 
larger cross-section is to be used, or whether a supplementary 
conductor is in a suitable manner to be connected with the 
old one, is best left to the judgment of the person entrusted 
with the installation. 

In coupling several dynamos in parallel to a common con- 
ductor, care must in all cases be taken to connect a dynamo to 
one already in operation only after it had been excited to the 
same voltage. If this were not done, the current of greater 



ELECTRO-PLATING ESTABLISHMENTS. 



173 



H 




174 ELECTRO-DEPOSITION OF METALS. 

electro-motive force of the dynamo in operation would flow 
from the main conductor to the other dynamo, and the first 
dynamo would thus be short-circuited by the brushes, com- 
mutator and armature of the second one. No current would 
pass into the baths, but the second dynamo would run as a 
motor. To prevent this, a switch has to be placed between 
every dynamo and the main conductor. If one dynamo 
already furnishes current, the second dynamo has at first to be 
set in operation with the switch open, until its voltmeter shows 
the same voltage as possessed by the other dynamo. The 
switch is then closed, and the desired current-strength gen- 
erated by means of the shunt-regulator. It is obvious that for 
coupling in parallel, only dynamos which yield the same 
voltage are suitable, while a difference in capacity as regards 
current-strength is no obstacle. 

The poles of a similar name of the various machines must 
of course be connected to one and the same circuit. 

Coupling of dynamos in series may become necessary when 
baths require a greater electro-motive force than can be fur- 
nished by a single machine,, for instance, in case baths are 
coupled one after the other. For coupling in series only 
dynamos which furnish with the same voltage the same current- 
strength are suitable. Coupling is effected so that the + pole 
of one dynamo is connected with the — pole of the other one, 
hence in the same manner as cells and accumulators are 
coupled. 

Coupling in series of dynamos may also be used if there are 
baths requiring great electro-motive force, for instance, for 
plating eh masse in the mechanical apparatus (see later on), 
while baths requiring a considerably lower electro-motive force 
are to be fed from the same source of current. 

In such case it is advisable to construct the conductors 
according to the three-wire system. One conductor is 
branched off from the -f- pole of one dynamo, the second from 
the — pole of the other dynamo, and the third, called the 
neutral or middle conductor, from the junction of the dyna- 



ELECTRO-PLATING ESTABLISHMENTS. 175 

mos coupled in series. Between the last-mentioned neutral 
conductor and an outside conductor is the lower electro- 
motive force as furnished by one dynamo, but between the 
two outside conductors, the sum of the electro-motive forces of 
both dynamos. Hence the baths requiring a large electro- 
motive force are to be coupled between the outside conductors, 
and the baths requiring a low electro-motive force between an 
outside and the neutral conductor. 

Ground plan of an electro-plating plant with dynamo. This 
in the most simple form is shown in Fig. 66. In order to 
make the sketch more distinct, the measuring instruments 
have been omitted. Their arrangement will be understood 
from what has been previously said, and from Fig. 66. 

NN 1 is a dynamo-electric machine of older construction. 
The resistance-board belonging to the machine, which is 
placed in the conductor, is indicated by No. 1, and is screwed 
to the wall. The main conductors, marked — and +, run 
along the wall, from which they are separated by wood, and 
consist of rods of pure copper 0.59 inch in diameter. The 
rods are connected with each other by brass coupling-boxes 
with screws. From the negative pole and the positive pole of 
the machine to the object-wire and anode-wire lead two wires, 
each 0.27 inch in diameter ; one end of each is bent to a flat 
loop and secured under the pole-screws of the machine, while 
the other ends are screwed into the second bore of the binding- 
screws screwed upon each conductor. To the right and left of 
the machine the baths are placed, Zn, indicating zinc bath ; 
M Ni, nickel baths ; Ku, copper cyanide bath ; Mg, brass 
bath ; S K, acid copper bath ; Si, silver bath ; and Go, gold 
bath. Each of the first-named five baths has its own resist- 
ance-board, designated by 2, 3, 4, 5, 6. However, before 
reaching the acid copper bath, and the silver and gold baths, 
the current is conducted through two resistance-boards, 7 and 
8. Since these baths require a current of only slight electro- 
motive force, it is necessary to place two, and in many cases 
even three or four resistance-boards, one after another, unless 



176 



ELECTRO-DEPOSITION OF METALS. 



it be preferred to feed these baths with a special machine of 
less voltage. 



Fig. 66. 



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ELECTRO-PLATING ESTABLISHMENTS. 177 

From Fig. 66 it will be seen that the current weakened by 
the resistance-boards 7 and 8 serves for conjointly feeding the 
acid-copper, silver, and gold baths. Hence, practically, only 
one bath can be allowed to work at one time, as otherwise 
each bath would have to be provided with as many resistance- 
boards as would be required for the reduction of the electro- 
motive force. For want of space the gold bath is placed in 
the sketch behind the silver bath ; but as their resistances are 
not the same, they must also be placed parallel. 

L is the lye-kettle. It serves for cleansing the objects by 
means of hot caustic potash or soda lye, from grinding and 
polishing dirt and oil. For larger plants the use of a jacketed 
kettle is advisable. By the introduction of steam in the jacket 
the lye is heated without being diluted. The same object is 
attained by placing a steam coil upon the bottom of the kettle. 
Of course, heating may also be effected by a direct fire. In- 
stead of the preparatory cleansing with hot lye, which saponi- 
fies the. oil, the objects may be brushed off with benzine, oil of 
turpentine or petroleum, the principal thing being the re- 
moval of the greater portion of the grease and dirt, so that the 
final cleansing, which is effected with lime paste, may not re- 
quire too much time and labor. It is also advisable to cleanse 
the objects, in one way or the other, immediately after grind- 
ing, as the dirt, which forms a sort of solid crust with the oil, 
is difficult to soften and to remove when once hard. 

The table which serves for the further cleansing of the 
objects has already been described on p. 161, and illustrated 
by Fig. 62. 

Referring again to Fig. 66, between the lye-kettle L and the 
box-table, is a frame, 14, for the reception of brass and copper 
wire hooks of various sizes and shapes suitable for suspending 
the objects in the bath. 

The reservoir W, filled with water, standing in front of the 
machine, serves for the reception of the cleansed and pickled 
objects, if for some reason or other they cannot be immediately 
brought into the bath. 
12 



178 



ELECTRO-DEPOSITION OF METALS. 



H W is the hot-water reservoir in which the plated objects 
are heated to the temperature of the hot water, so that they 
may quickly dry in the subsequent rubbing in the saw-dust 




box Sp. Before polishing the deposits, iron and steel objects 
are thoroughly dried in the drying chamber T(Fig. 66), heated 
either by steam or direct fire. By finally adding to the appli- 



ELECTRO-PLATING ESTABLISHMENTS. 



179 



ances a large table, 13, for sorting and tying the objects on the 
copper wires, and a few shelves not shown in the illustration, 
everything necessary for operating without disturbance will 
have been provided. 



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Figs. 67a and 67b show a plating room and method of con- 
necting dynamo, tanks and instruments according to the two- 



180 ELECTRO-DEPOSITION OF METALS. 

wire system as fitted up by The Hanson & Van Winkle Co., 
Newark, N. J. The arrangement will be readily understood 
from the illustrations, so that a detailed description is not 
necessary. 

The three-wire system of current distribution has been generally 
adopted in the larger plants where a variety of solutions are 
in use. The necessity of shortening time for deposit without 
deterioration of the quality of work has been apparent ; this 
condition is effected through the agitation of the solution, and 
the consequent employment of a higher voltage, with propor- 
tionate increase in the ampere current. The majority of 
plating dynamos in use are capable of delivering 4 to 6 volts 
only, and their use precludes the adoption of the newer labor- 
saving method. To meet the demands for a generator that 
will deliver a higher range of voltage, dynamos operating 
on the three-wire system are built which will deliver a range 
of voltage up to 12 volts or higher, if so desired. By the use 
of these dynamos it is possible to take from the machine volt- 
ages of two different strengths at the same time, the higher 
voltage being double that of the lower, and thus provide a 
high pressure for mechanical plating apparatus, basket work 
or agitated solutions, and at the same time operate solutions 
of a low voltage. 

In wiring for this system, three main line conductors are 
used, the positive and negative, or outside lines, and the 
neutral or middle line. In this method of wiring there is a 
saving of over 37 per cent, effected in the cost of copper, as it 
is not necessary to use conductors of so large a cross-section as 
would be the case in the ordinary two-wire system. 

Figs. 68a and 68b illustrate a three-wire system showing 
plating room wired for the usual plating tanks, and also 
mechanical plating apparatus. All necessary voltmeters, am- 
meters and rheostats are shown. 

Switch-boards. In the sketch, Fig. 66, the resistance-board 
belonging to each bath is secured to the wall in the immediate 
neighborhood of the bath. This arrangement has the advan- 



ELECTRO-PLATING ESTABLISHMENTS. 



181 



tage that the operator can, directly after suspending the objects, 
conveniently effect regulation from the bath itself. The 




182 



ELECTRO-DEPOSITION OF METALS. 



resistances and measuring instruments, as well as the switches, 
may, however, be also arranged alongside each other on a 
switch-board. Where a large number of baths are in opera- 



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tion, several such switch-boards will, of course, have to be 
provided to avoid the necessity of the operator, having to walk 
too great a distance from the bath to the switch-board. 



ELECTRO-PLATING ESTABLISHMENTS. 



183 



Fig. 69 shows such a switch-board, upon which are mounted 
the dynamo resistance, the resistance for the accumulator, two 
resistances for two baths, three amperemeters, a voltmeter with 
switch, current indicator, as well as switches for engaging and 
disengaging the machine as well as the accumulator. For the 
sake of neatness the conductors and connections are on the 
back of the switch-board. 

A marble slab with a wood rim is the best material for a 
switch-board. Marble or slate is absolutely required if the 
arrangements for starting the electro-motors of the aggregates 

Fig. 69. 




or transformers are mounted upon the switch-board. If, in 
such a case, the latter were of wood, there would be danger of 
ignition by reason of the heating of the spirals, etc. Wooden 
switch-boards may, however, be used for measuring instru- 
ment and resistances not especially subject to heating. 

The suggestions and directions given in the section " In- 
stallation with Cells " as regards regulation of current, meas- 
uring instruments, conductors, tanks for solutions, etc., apply 
also to installations with dynamos, and the reader is referred 
to that section. 



184 ELECTRO-DEPOSITION OF METALS. 

C. Installations and Accumulators. 

Only in rare cases will an electro-plating plant be operated 
by an accumulator alone. 

For larger establishments, where deposits requiring many 
hours for finishing are made, for instance, in copper and nickel 
galvanoplasty, silvering by weight, etc., the use of an accumu- 
lator, in addition to a dynamo, is of great advantage, since the 
process of depositing need not be interrupted during the noon 
intermission or, in case it is not finished in the evening, dur- 
ing the night, such interruptions affecting in various ways the 
quality of the deposit. 

However, even for depositing processes requiring a shorter 
time, for instance nickeling, an accumulator gives the oppor- 
tunity of turning the working power to better advantage. 
Suppose, for instance, that bicycle parts which are to be 
solidly nickeled have to remain in the bath for 1^- hours. 
However, the steam engine, and consequently the dynamo, 
are stopped at 12 M. (noon), and hence no objects can be 
brought into the bath after 10:30 a. m., as otherwise they 
would not be finished by noon, and an interruption in the 
nickeling process has to be avoided. If, however, an accumu- 
lator can during the noon hour be used for feeding the baths, 
objects can be suspended up to that time in the baths and 
taken from them finished when the noon-hour expires and 
operations are recommenced. The same can be done in the 
evening, and thus by the use of an accumulator the producing 
power of an electro-plating plant can be materially increased. 

If an accumulator is thus to be made use of, a dynamo of an 
adequately larger size has to be selected so that in addition to 
the depositing work, the accumulator can at the same time be 
charged by direct current from the dynamo. 

In establishments where the current is generated by a motor- 
generator or transformer fed from a central station, an accumu- 
lator is a good investment, since in this case the operating 
current is constantly at disposal and the motor-generators and 
ransformers can consequently run day and night. 



ELECTRO-PLATING ESTABLISHMENTS. 185 

Instead of feeding the baths and the accumulator simultane- 
ously with current from a larger dynamo, two dynamos may, 
of course, also be used, one of them supplying the baths and 
the other the accumulator. 

The magnitude of the performance of an accumulator de- 
pends on the current-strength which it is to yield for a certain 
time. As previously stated, the value ampere-strength X hours 
is called the ampere-hour capacity of an accumulator. Hence 
the question arises for how long the accumulator is to do the 
work of the dynamo while the latter is not running, and what 
current-strength is during this time to be transmitted from the 
accumulator to the bath. If now this ampere-hour capacity is 
known, as well as the maximum current-strength required for 
feeding the bath from the dynamo, we also know the current- 
strength which the dynamo must have. 

To explain this by an example, we will suppose that the bath 
requires at a maximum 200 amperes, and that the dynamo has 
to directly feed the bath for four hours and at the same time 
•charge a cell, which, when the dynamo stops, is to discharge 
for two hours with 200 amperes to the bath. The cell must 
therefore have a capacity of 400 ampere-hours, and taking into 
•consideration the fact that for charging at least 10 per cent, 
more charging current is necessary than corresponds to the 
discharging current, 440 amperes will have to be used for one 
hour in order to charge the cell, or 220 amperes for two hours, 
140 amperes for four hours. Since the dynamo, previous to 
being stopped, has directly to yield for four hours to the bath, 
200 amperes, there are four hours at disposal for charging 
the cell, and the dynamo must therefore have a capacity of 
200 + 110 = 310 amperes. 

The diagram Fig. 69 shows the connection of a plant as 
installed by the Electro-Chemical Storage Battery Co., of New 
York. 

By suitable manipulation of the switches and rheostats it is 
possible to make the following connections : 1. The dynamo 
alone can be used on the baths. 2. The batteries alone can 



186 



ELECTRO-DEPOSITION OF METALS. 
Fig. 70. 




ELECTRO-PLATING ESTABLISHMENTS. 187 

be used on the baths. 3. The dynamo can be used on the 
baths and the batteries charged with the excess-current, while 
at the same time steadying the dynamo current. 4. The 
dynamo and batteries can be used in multiple on the baths, 
giving a greatly increased capacity. 



CHAPTER V. 

PREPARATION OF THE METALLIC OBJECTS. 

As previously stated, the metallic objects to be plated have 
to undergo both a mechanical and chemical preparation, and 
each of these processes will be considered separately. 

A. Mechanical Treatment Previous to Electro-Plating. 

If the objects are not to be plated while in a crude state, 
which is but rarely feasible, the mechanical treatment consists 
in imparting to them a cleaner surface by scratch-brushing, or a 
smoother and more lustrous one by grinding and polishing. It 
may here be explicitly stated that scratch-brushing of plated 
objects is not to be considered a part of their preparation, 
since such scratch-brushing is executed in the midst of, or after 
the plating process, its object being to effect an alteration of 
the electro-deposits in more than one direction, and not the 
cleansing of the surface of the metallic base. The following 
directions, therefore, apply only to scratch-brushing of objects 
not yet plated. The scratch-brushing of electro-deposits will 
be considered later on. In regard to grinding, we have to deal 
with the subject only in so far as it relates to smoothing rough 
surfaces by the use of grinding powders possessing greater 
hardness than'the metal to be ground. With grinding in the 
sense of instrument-grinding, the primary object of which is to 
provide the instrument with a cutting edge, we have nothing 
to do. 

As some platers seem to have wrong ideas regarding the 
-electro-plating process, it may here be mentioned that the de- 
posit is formed exactly in correspondence with the surface of 
the basis-metal. If the latter has been made perfectly smooth 

(188) 



PREPARATION OF THE METALLIC OBJECTS. 



189 



by grinding and polishing, the deposit will be of the same 
nature; but if the basis-surface is rough, the deposit also will 
be rough. Hence it is wrong to suppose that by electro-plat- 
ing a rough surface can be converted into a lustrous one, and 
that pores, holes or scratches in the basis-metal can be filled 
by plating. In order to obtain a deposit which is to acquire 
high luster by polishing, it is absolutely necessary to bring 
the basis into a polished state by mechanical treatment. In 
doing this it is not necessary to go so far as to produce high 



Fig. 71. 



Fig. 72. 



Fig. 73. 



Fig. 74. 




luster, but fine scratches, which would be an impediment to 
attaining high luster after plating, must be removed. 

Scratch-brushing may be effected either by hand or by a 
scratch-brush lathe. For hand- work, scratch-brushes of more 
or less hard brass or steel wire, according to the hardness of 
the metal to be manipulated, are used. Various forms of 
brushes are employed, the most common ones being shown in 
the accompanying illustrations (Figs. 71 to 79). 

Fig. 78 shows a swing brush for frosting or satin finish, and: 



190 



ELECTRO-DEPOSITION OF METALS. 



Fig. 79 a goblet brush without stem of bristle and wire for 
use on inside of goblets, pitchers, urns, hollow ware, etc. 

In scratch-brushing it is recommended first to remove, or at 
least to soften, the uppermost hard and dirty crust (the scale) 
by immersing the objects in a pickle, the nature of which 
depends on the variety of metal, so that a complete removal of 
all impurities and non-metallic substances may be effected by 
means of the scratch-brush in conjunction with sand, pumice- 
stone, powder, or emery. The composition of pickles will be 



Fig. 75. 



Fig. 7 



Fig. 77. 




given later on. Scratch-brushing is complete only when the 
article shows a clean metallic surface, otherwise the brushing 
(scouring) must be continued. Scratch-brushes must be care- 
fully handled and looked after, and their wires kept in good 
order. When they become bent they have to be straightened, 
which is most readily effected by several times drawing the 
brush, held in a slanting position, over a sharp grater such as 
is used in the kitchen. By this means the wires become dis- 
entangled and straightened out. 



PREPARATION OP THE METALLIC OBJECTS. 



191 



Hand scratch-brushing being slow and tedious work, large 
establishments use circular scratch-brushes which are attached 
to the spindle of a lathe. These circular brushes consist of 
round wooden cases in which, according to requirement, 1 to 
6 or more rows of wire bundles (see Fig. 80) are inserted. 

Brushes with wooden cases are, however, more suitable for 
scratch-brushing deposits than for cleansing the metallic base, 
since for the latter purpose a more energetic pressure is usually 
applied, in consequence of which the bundles bend and even 
break off, if the wire is anyways brittle. For cleansing pur- 
poses a circular scratch-brush, which the workman can readily 
refurnish with new bundles of wire, deserves ' the preference. 
It is constructed as follows : A round iron disk about 0.11 inch 
thick, and from 5f to 7f inches in diameter, is provided in 



Fig 




the center with a hole so that it can be conveniently placed 
upon the spindle of the lathe. At a distance of from 0.19 to 
0.31 inch from the periphery of the disk, holes 0.079 to 0.11 
inch in diameter are drilled, so that between each two holes 
is a distance of 0.15 inch. Draw through these holes bundles 
of wire about 3.93 inches long, so that they project an equal 
distance on both sides." Then bend the bundles towards the 
periphery, and on each side of the iron disk place a wooden 
disk 0.31 to 0.39 inch thick. The periphery of the wooden 
disk, on the side next to the iron disk, should be turned semi- 
annular, so that the wooden disks when secured to the spindle 
press very lightly upon the wire bundles, and the latter re- 
main very mobile. When a circular scratch-brush constructed 



192 ELECTRO-DEPOSITION OF METALS. 

in this manner and secured to the lathe is allowed to make 
from 1800 to 2000 revolutions per minute, the bundles of wire, 
in consequence of the centrifugal force, stand very rigid, but 
being mobile will give way under too strong a pressure with- 
out breaking off, and can thus be utilized to the utmost. 
When required, the iron disk can be refurnished with wires in 
less than half an hour. An error frequently committed is that 
the objects to be cleansed are pressed with too heavy a pres- 
sure against the wire brushes. This is useless, since only the 
sharp points of the wire are effective, the lateral surfaces of the 
bundles removing next to nothing from the articles. 

Brushes. A definition of these instruments is unnecessary, 
and we shall simply indicate the various kinds suitable to the 
different operations. 

The fire-gilder employs, for equalizing the coating of amal- 

Fig. 81. Fig. 82. Fig. 83. 




gam, a long-handled brush, the bristles of which are long and 
very stiff. The electro-gilder uses a brush (Fig. 81) with long 
and flexible bristles. 

For scouring with sand and pumice-stone alloys containing 
nickel, such as German silver, which are difficult to cleanse in 
acids, the preceding brush, with smaller and stiffer bristles, is 
used. 

The gilder of watch-works has an oval brush (Fig. 82), with 
stiff and short bristles for graining the silver. 

The galvanoplastic operator, for coating moulds with black- 
lead, besides a number of pencils, uses also three kinds of 
brushes — the watchmaker's (Fig. 83), a hat brush, and a 
blacking-brush. The bronzer uses all kinds of brushes. 

Brushes are perfectly freed from adherent grease by washing 
with benzine or carbon disulphide. 



PREPARATION OF THE METALLIC OBJECTS. 



193 



In large establishments engaged in electro-plating cast-iron 
without previous grinding, the use of the sand-blast, in place of 
the circular wire brush, has been introduced with great advan- 
tage. Objects with deep depressions, which cannot be reached 
with the scratch-brush, as well as small objects, which cannot 
be conveniently held in the hand and pressed against the re- 
volving scratch-brush, can be brought by the sand-blast into a 
state of sufficient metallic purity for the electro-plating process. 

However, while circular scratch-brushes impart to the ob- 

Fig. 84. 




jects a certain, though not very great luster, the metal por- 
tions are matted by the sand-blast, and the latter is frequently 
employed for matting entire lustrous surfaces or for produc- 
ing contrasts, for instance,.mat designs upon lustrous grounds, 
or vice versa. 

A large variety of types of sand-blasting machines have 
been introduced, a number of them having been designed for 
use in cleansing large iron castings for engineering work. A 
sand-blast suitable for the electro-plater's purpose is shown in 
Fig. 84. It is very compact and convenient for use in a 
14 



194 



ELECTKO-DEPOSITION OF METALS. 



limited floor space. The necessary pressure is obtained by 
compressed air. The compressed air, the pressure of which 
should be at least equal to that of a column of water 18J 
inches high, passes through the blast-pipe A into a nozzle 
Tunning horizontally through the machine, carries along a 
jet of sand, and hurls the latter upon the objects placed under- 
neath the nozzle. The objects are placed upon sheet-iron 
plates or in sheet-iron boxes and very slowly passed below the 
nozzle, the motion being effected by the shafts BB with the 
use of rubber belts. To avoid dust, the machine is provided 
with a jacket of sheet-iron or wood ; a few windows enable the 
operator to watch the progress of the operation. 

The uses to which a sand-blast can be put are very numer- 

Fig. 85. 




ous. The frosting or satin-finishing of silverware and other 
articles, engraving or stenciling of metal or glass, inlaying, 
removing scale, etc., the nature of the work being governed 
by the fineness of the sand used as well as the pressure. 

If a clean metallic surface is at one time to be given to a 
large number of small articles, such as buckles, steel beads, 
metal buttons, steel watch chains, ferrules, etc., a tumbling 
barrel or drum is frequently used (Fig. 85). It generally con- 
sists of a cylindrical or polygonal box having a side door for 
the introduction of the work, together with sharp sand or 
emery, and is mounted horizontally on an axis furnished with 
a winch or pulley, so as to be revolved either by hand or 
power, as may be desired. In order to prevent certain objects, 



PREPARATION OF THE METALLIC OBJECTS. 195 

like hooks for ladies' dresses and the like, from catching each 
•other and combining into a mass, a number of nails or 
wooden pegs are fixed in the interior of the drum. 

For ordinary polishing the articles are brought into the 
tumbling barrel together with small pieces of leather waste 
(leather shavings), and taken out in one or two days. How- 
ever, to produce an actualty good polish a somewhat more 
complicated method has to be pursued. The articles are first 
freed from adhering scale by washing in water containing 5 
per cent, of sulphuric acid, then rinsed and dried in a drying 
chamber, or in a pan over a fire. They are next brought into 
the tumbling barrel together with sharp sand, such as is used in 
glass-making, and revolved for about 12 hours, when they are 
taken from the barrel and freed from the admixed sand by sift- 
ing. They are then returned to the barrel, together with soft, 
fibrous sawdust, to free them from adhering sand, and at the 
same time to give them a smoother surface. They are now 
again taken from the barrel, freed from sawdust, and returned 
to the barrel, together with leather shavings. They now re- 
main in the barrel until they have acquired the desired polish, 
which, according to the size and shape of the articles and the 
degree of polish required, may frequently take two weeks or 
more. , Articles of different shapes and sizes are best treated 
together, time being thereby saved. The process is also accel- 
erated by adding some fat oil to the leather shavings, which, 
■of course, must be omitted when, after long use, the shavings 
have become quite greasy. The barrel should be filled about 
half full, otherwise the articles do not roll freely, and polish- 
ing is retarded. On the other hand, when the barrel is less 
than half full there is danger of the articles bending, or in 
•case they are hardened, for instance buckles, of breaking. 

For many purposes polishing in the tumbling barrel is of 
great, advantage, since, independent of its cheapness, the sharp 
edges of the articles are at the same time rounded off. How- 
ever, with articles the edges of which have to remain sharp, 
the process cannot be employed. 



196 



ELECTRO-DEPOSITION OF METALS. 



Fig. 86. 



The tumbling barrel in which the articles are treated with 
sand cannot be used for polishing with leather shavings, it 
being next to impossible to free it entirely from sand. The 
barrels should make from 50 to 70 revolutions per minute; if 
allowed to revolve more rapidly, the articles take part in the 
revolutions without rolling together, which, of course, would 
prevent polishing. 

The brightening of articles of iron and steel may be simpli- 
fied by using water to which 1 per cent, of sulphuric acid has 
been added. The barrel used for the purpose must, of course, 
be water-tight. By the addition of sand the process is acceler- 
ated. Nickel and copper blanks for coins are also cleansed in 
this manner. They are brought into the tumbling barrel, 
together with a pickling fluid, and, when sufficiently treated, 
are taken out, rinsed, dried in sawdust, and finally stamped. 
Fig. 86 shows a form of an adjustable, oblique tumbling 

barrel, adapted to clean, smooth 
brighten, and polish nearly every 
variety of iron and brass goods. The 
simplicity and durabilit} 7 of the con- 
struction and the rapidity with which 
the work is done are distinct advan- 
tages. The machine can be used 
wet or dry. It is adjustable by screw 
and wheel to any working elevation 
up to 50°. The machine shown in 
the illustration is designed to carry 
a barrel 24 inches in diameter, but 
larger or smaller barrels can be used. 
Grinding. Wooden wheels cov- 
ered with leather coated with emery of various degrees of fine- 
ness are almost exclusively used for grinding metallic objects 
preparatory to the plating process. The wooden wheels are 
made of thoroughly-seasoned poplar, in the manner shown 
in Fig. 87. The separate pieces are radially glued together, 
and upon each side in the center a strengthening piece is. 





PREPARATION OF THE METALLIC OBJECTS. 197 

glued and secured with screws, so that each segment of the 
wheel is connected with the strengthening piece. The center 
of the wheel is then provided with a 
hole corresponding to the diameter of the 
spindle of the grinding lathe, to which it 
is secured by means of wedges. The 
periphery, as well as the sides, is then 
turned smooth. A good quality of 
leather, previously soaked in water and 
cut into strips corresponding to the width 
of the wheel is then glued to the periph- 
ery, and still further secured by pins of soft wood. When the 
glue is dry the wheel is again wedged upon the spindle and 
the leather case fully turned; it is then ready for coating with 
■emery. 

With the use of grinding wheels of oak or walnut, covering 
with leather may be omitted, and the emery can be applied 
directly to the wheels. However, leather-covered wheels are 
to be preferred since, by reason of their elasticity, better results 
in grinding are obtained than with uncovered wheels of the 
above-mentioned varieties of wood. 

For grinding soft metals, hard, impregnated felt wheels 
<c set up" with glue and emery are also employed. 

For grinding profiled articles preference should be given to 
wheels without leather covering, and the grinding surface 
should be fitted to the profile of the article to be ground by 
cutting with a turning tool. 

Grinding wheels of paste-board and of cork waste have re- 
cently been introduced. The former are made by coating on 
both sides thin, round disks of paste-board with glue mixed 
with emery, and then gluing a sufficient number of such 
•disks one upon the other to form a wheel of the desired width. 
The wheel is finally subjected to strong pressure under a 
hydraulic press, and dried. However, as these wheels have 
•disappeared from commerce, it may be assumed that they 
have not stood the test in practice. The same may be said of 



198 



ELECTRO-DEPOSITION OF METALS. 



Fig. 88. 




mm 



III 

ill 



cork wheels. The so-called elastic wheel has also not an- 
swered the demands made in practice. The cementing mater- 
ial in the case consisted of a gum or 
rubber-like mass, which to be sure 
imparted great elasticity to the- 
wheel, but when the latter became 
hot during grinding, the mass soft- 
ened and smeared. 

The so-called reform wheel, Fig. 
88, has a better prospect of general 
introduction. The leather covering 
does not consist of a single strap, but 
pieces of leather, 3 to 5 millimeters 
thick, are placed alongside each other 
and secured by means of a sort of 
dove-tailing to an iron rim, which 
is screwed upon the wooden disk. According to the length 
of the pieces of leather a greater or smaller degree of elasticity 
is attained. One covering lasts at least five to eight times 
as long as the covering w T ith leather straps, and leather-waste, 
otherwise of scarcely any value, may be employed for the 
covering. 

For grinding soft metals, hard impregnated felt wheels 
coated by means of glue with emery are also used. 

For gluing with emery three different kinds of emery are 
used, a coarse quality (Nos. 60 to 80) for preparatory grind- 
ing, a finer quality (No. 00) for fine grinding, and the finest 
quality (No. 0000) for imparting luster. The wheels thus 
coated are termed respectively " roughing wheel," "medium 
wheel," and " fine wheel." With the first the surface of the 
objects are freed from the rough crust. The coarse-grained 
emery used for this purpose, however, leaves scratches, which 
have to be removed by grinding upon the medium wheel until 
the surfaces of the objects show only the marks due to the 
finer quality of emery, which are in their turn removed by 
the fine wheel. 



PREPARATION OP THE METALLIC OBJECTS. 199 

In most cases brushing with a circular bristle brush may be 
substituted for the last grinding, the articles being moistened 
with a mixture of oil and emery No. 0000. Care must be had 
not to execute the brushing nor the grinding with the finer 
quality of emery in the same direction as the preceding grind- 
ing, but in a right angle to it. 

Treatment of the grinding wheels. — The coating of the rough- 
ing wheels with emery is effected by applying to them a 
good quality of glue and rolling them in dry, coarse emery 
powder. For the medium and fine wheels, however, the emery 
is mixed with the glue and the mixture applied to the leather. 
When the first coat is dry, a second is applied, and finally a 
third. The whole is then thoroughly dried in a warm place. 
Before use, a piece of tallow is held to the revolving disc for 
the purpose of imparting a certain greasiness to it, and in order 
to remove any roughness due to an unequal application of the 
emery, it is smoothed by pressing a smooth stone against it. 
While the preparatory grinding upon the roughing wheel is 
executed dry, i. e., without the use of oil or fat, in fine grinding, 
the objects are frequently moistened with a mixture of oil and 
the corresponding No. of emery. When the layer of emery is 
used up, the remainder is soaked with warm water and scraped 
off with a dull knife. The leather of the disks on which oil or 
tallow has been used is then thoroughly rubbed with caustic 
lime or Vienna lime * to remove the greasiness, which would 
prevent the adherence of the layer of glue and emery to be 
applied later on. When the leather is thoroughly dry a fresh 
layer of emery may at once be applied. 

To prevent the leather from absorbing an excess of water 
when moistening the old layer of glue and emery for the pur- 
pose of softening it, it is advisable to apply moderately wet 

* Vienna lime is prepared from a variety of dolomite which is first burned, then 
slaked, and finally ignited for a few hours. It consists of lime and magnesia, and 
should be kept in well-closed cans, as otherwise it absorbs carbonic acid and 
moisture from the air, and becomes useless. 



200 



ELECTRO-DEPOSITION OF METALS. 



clay to the layer and allow it to remain for a few hours when 
the emery can be readily scraped off. 

A very useful machine for removing emery and glue from 
worn, leather-covered wood polishing wheels is shown in Fig. 
89. The compartment is filled with water until it just touches 
the lower part 'of the rollers. Then by placing the worn 
wheels on the rollers and allowing the machine to run for a 
short time all the glue and emery will be removed without 
damaging or loosening the leather covering. The rollers 
carry just enough water to properly feed the face of the wheels, 
and the friction caused by the weight of the wheels revolving 



Fig. 89 




on the rollers quickly forces off the emery and glue. Allow 
the wheels to dry in the ordinary temperature ; do not subject 
them to heat. 

Grinding lathes. For use, the grinding wheels are wedged 
upon a conical cast-steel spindle provided with a pulley and 
running in bearings, as plainly shown in Fig. 90. The cast- 
iron standards are screwed to the floor ; the wooden bearings 
can be shifted forward and backward by wedges and secured 
in a determined position by a set-screw, thus facilitating the 
removal of the spindle after throwing off the belt. The 
wheels being wedged upon a conical spindle, always run 



PREPARATION OF THE METALLIC OBJECTS. 201 

centrically. Changing of the wheels requires but a few 



Fig. 90. 




seconds, and on account of the slight friction of the points of 

Fig. 91. 




the spindle in the wooden bearings, the consumption of power 
is very slight. 



202 



ELECTRO -DE POSITION OF METALS. 



To avoid the necessity of throwing off the belt while chang- 
ing the grinding wheels, double machines (Fig. 91) are used, 
the principle of conical spindles being, however, preserved. 
The shaft is provided with loose and fast pulley and coupling 
lever. 

Fig. 92 illustrates a similar machine with ring-oiling. 

Fig. 93 represents a belt-attachment combined with a double 
grinding lathe, as constructed by the firm of Dr. G. Langbein 
& Co. The apparatus can be readily secured by means of 
screws to the lathe, and is readily removed. It allows of 

Fig. 92. 




grinding-wheels, brushes, etc., being attached to both ends of 
the shaft, while the belt can at the same time be used. 

Electrically-driven grinding motors have been previously re- 
ferred to. Fig. 94 shows a grinder of this type manufactured 
by The Hanson & Van Winkle Co., Newark, N. J. It is of 
the ribbed type, and is furnished in various sizes. The switch, 
starting box and regulator are contained within the stand, 
with the operating handles extending through a suitable open- 
ing. An important feature of this machine is the ability of 



PREPARATION OF THE METALLIC OBJECTS. 



203 



the operator to regulate the speed of the wheels, running them 
at the speeds most suitable for the work in hand. This regu- 
lation of the speed is accomplished by the simple movement 
of a handle, the speed remaining practically constant at any 
point. t 

A smaller type of the same machine is very suitable for use 
by manufacturers, jewelers, dentists, instrument makers, etc. 

Fig. 93. 




• These grinding motors, as well as the polishing motors to-' 
be described later on, have the advantage of occupying no 
more space than that is usually required by a belt-driven 
lathe, while the full motive power is applied, without loss, 
directly to the grinding wheels. They also possess the ad- 
vantage of being portable, and in a few moments' time can be 



204 



ELECTRO-DEPOSITION OF METALS. 



moved to any part of the factory that may be best suited for 
the purpose required, making it possible to take the motor to 
the work when desired, instead of bringing the work to the 
motor. 

Execution of grinding and brushing. Grinding is executed 
by pressing the surfaces to be ground against the face of the 
wheel, moving the objects constantly to and fro. The opera- 
tion requires a certain manual skill, since, without good 
reason, no more should be ground away on one place than on 

Fig. 94. 




another. Special care and skill are required for grinding 
large round surfaces. 

If the objects are to be treated with the fine wheel, fine 
grinding is succeeded by brushing with oil and emery by 
means of circular brushes formed of bristles set in disks of 
wood. Genuine bristles being at present very expensive, 
vegetable fiber, so-called fibers, has been successfully substi- 
tuted for them, the wooden wheel being replaced by an iron 
case, in the bell-shaped cheeks of which the fiber-bundles are 
secured by means of strong nuts. Before use it is advisable to 



PREPARATION OP THE METALLIC OBJECTS. 



205. 



saturate the fiber-bundles with oil in order to deprive them of 
their brittleness, and thus improve their lasting quality. 

The grinding lathe (Fig. 95) is provided with a tampico 
brush, this fiber being particularly adapted for rough, quick 
work. It can, of course, just as well be placed upon the con- 
ical spindles of double machines. The iron case is provided 
with a conical hole corresponding exactly to the conical spin- 
dle, the large frictional surface preventing the turning of the 
brush upon the spindle, or its running off. 



Fig. 95. 



Fig. 96. 





In regard to grinding the various metals, the procedure, 
according to the hardness of the metal, is as follows :. 

Iron and steel articles are first ground upon the roughing 
wheel, then fine-ground upon the medium wheel, and finally 
upon the fine wheel, or brushed with emery with the circular 
brush. Very rough iron surfaces may first be ground upon 
solid emery wheels before being worked upon, the roughing 
wheel. 

For depressed surfaces which cannot be reached with the 
large emery wheels, small walrus-hide wheels coated with glue 
and emery are placed upon the point of the spindle of a 
polishing lathe. 



206 



ELECTRO-DEPOSITION OF METALS. 



Brass and copper castings are first ground upon roughing 
wheels which have lost part of their sharpness and will no 
longer attack iron. They are then ground fine upon the 
medium wheel, and finally polished upon cloth or felt wheels 
(bobs). (See below under "Polishing.'") 

Sheets of brass, German silver and copper, as furnished by 
rolling-mills, are only brushed with emery and then polished 
with Vienna lime or rouge upon bobs. 

Zinc castings, as, for instance, those produced in lamp fac- 
tories, are first thoroughly brushed by means of circular 
brushes and emery, and then polished upon cloth bobs. 



Fig. 97. 



Fig. 





Sheet zinc is only polished with Vienna lime and oil upon 
cloth bobs secured to the spindle shown in Fig. 101. 

Polishing. — As will be seen from the foregoing, polishing 
serves for making the articles ready, i. e., the final luster is 
imparted to them upon soft polishing wheels with the use of 
fine polishing powder. The polishing wheels or bobs of fine 
felt, shirting, or cloth, are secured to the polishing lathe, and, 
according to the hardness of the metal to be polished, make 



PREPARATION OF THE METALLIC OBJECTS. 207 

2000 to 2500 revolutions per minute. A foot-lathe, such as is 
shown in Fig. 96, makes generally not over 1800 revolutions 
per minute. Cloth bobs are made by placing pieces of cloth 
one upon another in the manner described under " Nickeling 
of sheet zinc," cutting out the center so as to correspond to 
the diameter of the spindle, and securing the disks of cloth by 
means of nuts between two wooden cheeks upon the spindle of 
the polishing lathe. In place of cloth bobs, solid wheels of 
felt or wooden wheels covered with a layer of felt may be used, 
especially for polishing smooth objects without depressions, 
the fineness and softness of the felt depending on the degree 
of polish to be imparted and the hardness of the metal to be 
manipulated. 

An excellent polishing-wheel is the Union canvas wheel, 
made by the Hanson & Van Winkle Co., of Newark, N. J. 
It is shown in Fig. 97. It is not glued, but by a special 
process the weight is reduced, the elasticity and flexibility are 
increased, and a cloth face is obtained, which combined with 
the glue, presents a surface that will hold emery better than 
any other wheel. Being of a flexible nature, it easily adjusts 
itself to the irregularities of the work. No special skill is re- 
quired to use it, and there is less tendency to " gouge " the 
work or spoil design. The wheel will do more work with one 
setting-up than any other. It is durable and easily kept in 
balance. 

Fig. 98 shows the universal polishing wheel made by the 
Hanson & Van Winkle Co. This wheel is superior in every 
way. It is practically universal and decidedly economical. 
It can be used for " roughing," " fining ", or " greasing." It 
retains its shape — does not rag out, and will stay in balance 
almost indefinitely. It is resilient and remains so until nearly 
worn out. A finer grade of emery can be used, and the 
emery can be washed off and a new face, fine, smooth, and 
glazed, can be obtained for another setting up. The wheel 
will not burn the surface of the metal and in consequence a 
better "color" after plating is obtained. It is made in three 
grades; soft, medium and hard. 



208 ELECTRO-DEPOSITION OF METALS. 

Another wheel of great flexibility and elasticity is the wal- 
rine wheel manufactured by the same firm. On account of 
its flexibility and elasticity, combined with its hardness, it is 
recommended for hard grinding, and the fact that its face can 
be turned to any shape — at the same time preserving all the 
characteristics of hide wheels — will place it before sea-horse 
or walrus on its merits. One advantage of this wheel is its 
pliability, which allows it to adjust itself to any inequalities 
in the coat of emery, and consequently it wears evenly, and 
being lighter than any other serviceable wheel, it is much less 
liable to injure lathe bearings. 

Double polishing lathes according to American patterns, 
Figs. 99 and 100, are used for polishing objects of not too 
large dimensions. These polishing lathes are manufactured 

Fig. 99. 




in several sizes, the largest capable of using wheels 15 inches 
diameter and 5 inches face. Fig. 99 shows a 10-inch polish- 
ing head to be screwed to a bench. 

Fig. 100 illustrates a 14-inch ring-oiling polishing machine. 
The head is constructed so as to give plenty of room between 
the wheels and the column, thus making the machine of 
special advantage where awkward pieces are to be handled, as 
bicycle, chandelier, and similar classes of work. The bear- 
ings provided are peculiar to the machine, the boxes being so 
constructed that the spindle has four bearings, thus affording 
a good support and making the machine a stiff and durable- 
one. 



PREPARATION OF THE METALLIC OBJECTS. 209 

The polishing lathe shown in Fig. 101 serves chiefly for 

Fig. 100. 




polishing large sheets, the latter being placed upon a smooth, 

Fig. 101. 



wooden support which rests upon the knees of the workman, 
as will be described later on in speaking of nickeling sheet-zinc. 
14 



210 



ELECTRO-DEPOSITION OF METALS. 



Fig. 102 shows an independent spindle-polishing and buff- 
ing lathe manufactured by The Hanson & Van Winkle Co., 
Newark, N. J. In designing this lathe further demands for 
economy, viz., power, shafting and belting have been antici- 
pated. Countershafts, loose pulleys and incidental belting are 
dispensed with. To accomplish this, a single driving pulley 
and double friction cones, securely housed in the lathe head,, 
as shown in the illustration, are used on the lathe. 

Fig. 102. 




The forged steel clutches are operated by small hand levers^ 
above the casing. A study of the illustration will show the 
great strength and large provision for wear in the double fric- 
tion cones, as well as the spindle bearings, and the means for 
oiling. 

The lathe spindle is of large diameter, carefully ground and 
polished ; it runs smoothly and noiselessly and without end 
play. Throwing off the clutch brings a brake into action and' 



PREPARATION OF THE METALLIC OBJECTS. 211 

stops the spindle instantly, while the reverse motion releases 
the brake and starts the spindle immediately. This is done 
at either end without interference or waiting ; as a result there 
is no lost time for either operator, which means a saving of 
from one to three hours per day. 

The pedestal flares at the back so that the latter can be 
belted from below, a method now used in many shops, and 
always to be preferred, as it gives a room entirely free of belts. 

Electrically-driven polishing and buffing lathes are now in 
frequent use. The high speed at which emery and polishing 

Fig. 103. 




wheels are run necessitates tight belts, heated bearings, and the 
dirt carried by the belt. All this is overcome in these ma^- 
chines. They can be placed so as to secure the best light, the 
speed is constant, and no power is used in driving the counter- 
shaft when not in use. The machines are furnished with and 
without stand. 

Fig. 103 shows a type of polisher manufactured by the Han- 
son & Van Winkle Co. It has all the good points of the 
grinder (Fig. 94) manufactured by the same firm. 



212 



ELECTRO-DEPOSITION OF METALS. 



The belt-strapping attachment or endless-belt machine shown 
in Fig. 104 is made by the above-mentioned firm. It is sim- 
ple in construction and easily operated. It can be used to 
great advantage by manufacturers of bicycles and bicycle 
parts, brass cocks, and other plumbers' fittings, gas fixtures, 
grate and fender work, while for cutlery it seems almost indis- 
pensable. The attachment complete consists of a 12-inch and 
6-inch diameter flanged pulley, 2J inches between flanges, 
with standard and adjusting arms. 

No shop is now complete without one or more flexible shafts 
for grinding, polishing and buffing. It will in many ways be 



Fig. 104. 




found a profitable and economical device. For cleaning and 
grinding heavy castings, for polishing and buffing all metal 
and glass, it is an indispensable tool where power is or can be 
used to advantage. These shafts are made in standard sizes, 
from J-inch diameter core, suitable for very light work, to 1J- 
core, capable of driving a 3-inch drill in iron or steel. 

Polishing materials. — According to . the hardness of the 
material to be polished, rouge (ferric oxide, colcothar) tripoli, 
Vienna lime, etc., in the state of an impalpable powder, and 
generally mixed with oil, or sometimes with alcohol, are used 
as polishing agents. For hard metals, an impalpable rouge of 



PREPARATION OP THE METALLIC OBJECTS. 21 3 

great hardness (No. F of commerce), is employed, for softer 
metals, a softer rouge (No. FFF), or Vienna lime, tripoli, etc. 

It is of advantage to melt the rouge with stearine and a 
small quantity of tallow, and. cast the mixture in moulds with 
the aid of strong pressure. The sticks thus formed are suffi- 
ciently greasy to render the use of oil superfluous. In order 
to impregnate the surface of the polishing bob with the polish- 
ing material, hold one of the sticks for a second against the- 
revolving wheel, and then polish the objects by pressing them 
against the wheel, diligently moving them to and fro. The 
polishing bob must not be too heavily impregnated with rouge, 
since a surplus of the latter smears instead of cutting well. 

In polishing with Vienna lime it is expedient to moisten the 
objects to be polished with stearine oil, and saturate the polish- 
ing wheels by pressing a piece of Vienna lime against them. 
However, this causes a great deal of dust, which not only 
incommodes the workman, but is also injurious to the respira- 
tory organs. It is therefore recommended to remove the dust 
by means of an exhauster. 

Another process of polishing, called burnishing, is executed 
by means of tools usually made of steel for the first or ground- 
ing process, or of a very hard stone, such as agate or blood- 
stone, for finishing.. Burnishing is applied to the final polish- 
ing of deposits of the noble metals, and will be referred to 
later on. 

B. Mechanical Treatment During and After Electro-plating. 

In this connection scratch-brushing the deposits will be first 
considered, the object of this operation being, on the one hand 
to promote the regular formation of certain deposits, and, on 
the other, to affect the physical properties of the deposits, and 
finally to ascertain whether the deposit adheres to the basis- 
metal. 

If it is noticed by the irregular formation of the deposit that 
the basis-metal has not been cleaned with sufficient care by the- 
preparatory scratch-brushing, the object has to be taken from 



214 ELECTRO-DEPOSITION OF METALS. 

the bath and the defective places again scratch-brushed with 
the application of water and sand, or pumice stone, when the 
object is again pickled and replaced in the bath. 

On the other hand, the deposits always form more or less 
porous, they having, so to say, a net-like structure, though it 
may not be visible to the naked eye. By scratch-brushing, 
the meshes of the net are made Closer by particles of metals 
being forced into them by the brush, and the deposit is thus 
rendered capable of receiving additional layers of metal. 
Furthermore, by scratch-brushing, dull deposits acquire a 
certain luster, which is enhanced by the subsequent polishing 
process. Finally, by an unsparing application of the scratch- 
brush, it will be best seen whether the union of the deposit 
with the basis-metal is sufficiently intimate to stand, without 
becoming detached, the subsequent mechanical treatment in 
polishing. 

According to the object in view, and the hardness of the de- 
posit to be manipulated, scratch-brushes of steel or brass wire 
are chosen. For nickel, which, as a rule, requires scratch- 
brushing least, and chiefly only for the production of very 
thick deposits, steel wire of 0.2 millimeter thickness is taken ; 
for deposits of copper, brass, and zinc, brass wire of 0.2 milli- 
meter ; for silver, brass wire of 0.15 millimeter ; and for gold, 
brass wire of 0.07 to 0.1 millimeter. Scratch-brushing is 
seldom done dry. The tool as well as the pieces should be 
constantly kept wet with liquids, especially such as produce a 
lather in brushing, for instance, water and vinegar, or sour 
wine, or solutions of cream of tartar or alum, when it is de- 
sired to brighten a gold deposit which is too dark. However, 
the liquid most generally used is a decoction of licorice-root, 
of horse-chestnut, of marshmallow, of soap-wort, or of the bark 
of Panama-wood, all of which, being slightly mucilaginous, 
allow of a gentle scouring with the scratch-brush, with the 
production of an abundant lather. A good adjunct for 
scratch-brushing is a shallow wooden tub containing the 
liquid employed, with a board laid across it nearly level with 



PREPARATION OF THE METALLIC OBJECTS. 215 

the edges, which, however, project a little above. This board 
serves as a rest for the pieces. 

The hand scratch-brush, when operating upon small ob- 
jects, is held by the workman in the same manner as a paint 
brush, and is moved over the object with a back and forward 
•motion imparted by the wrist only, the forearm resting on the 
-edge of the tub. For larger objects, the workman holds his 
•extended fingers close to the lower part of the scratch-brush, 
so as to give the wires a certain support, and, with raised 
•elbow, strikes the pieces repeatedly, at the same time giving 
the tool a sliding motion. When a hollow is met with, which 
cannot be scoured longitudinally, a twisting motion is im- 
parted to the tool. 

Scratch-brushing by means of circular scratch-brushes is 
•effected in a lathe. The lathe-brush is mounted upon a 
spindle and is provided above with a small reservoir to con- 
tain the lubricating fluid, a small pipe with a tap serving to 
conduct the solution from this to a point immediately above 
the revolving brush. The top of the brush revolves towards 
the operator, who presents the object to be scratch-brushed to 
the bottom. The brush is surrounded by a wooden cage or 
screen to prevent splashing. To protect the operator against 
the water projected by the rapid motion, there is fixed to the 
top of the frame a small inclined board, which reaches a little 
lower than the axis of the brush without touching it. This 
board receives the projected liquid, and lets it fall into a zinc 
trough, which forms the bottom of the box. Through an 
outlet provided in one of the angles of the trough, a rubber 
tube conveys the waste liquid to a reservoir below. After 
scratch-brushing every trace of the lubricating liquid must be 
washed away before placing or replacing the objects in the 
bath. 

Drying. — The finished plated objects are first rinsed in clean 
-water to remove the solutions constituting the bath adhering 
to them. They are next immersed in hot water, where they 
remain until they have acquired the temperature of the water, 
and are then quickly dried in the manner described on p. 163. 



216 ELECTRO-DEPOSITION OF METALS. 

A very good method of freeing nickeled objects from all 
moisture which may have collected in the pores is to immerse 
them for about ten minutes in boiling linseed oil, and, after 
allowing them , to drain off, to remove the adhering oil by 
rubbing with sawdust. According to some electro-platers, the 
deposit of nickel thus treated loses its brittleness and will stand 
bending several times, for instance, wire, sheets, etc., without 
breaking. Experiments m-ade by Dr. George Langbein did 
not confirm these statements, but the security against rust of 
nickeled-iron objects is found to be considerably enhanced by 
boiling in linseed oil. 

Production of high luster. — When dry, the plated objects are 
highly polished, this being effected by means of polishing 
bobs of fine felt, cloth or flannel, with the use of polishing 
compositions, vienna lime, etc., or by burnishing with tools of 
steel and of agate or blood-stone. 

Nickel deposits are almost without exception polished upon 
cloth or felt bobs with rouge or Vienna lime. 

Copper and brass deposits are polished with fine flannel bobs,, 
the polishing powder being applied very sparingly. Deposits 
of tin are generally only scratch-brushed, it being impossible 
10 impart great luster to this metal by polishing with bobs. 
After drying, the deposit is polished with whiting. Deposits- 
of gold and silver as well as of platinum are polished by burn- 
ishing, the steel burnisher being used for the grounding pro- 
cess, and an agate or blood-stone burnisher for finishing. The 
operation of burnishing is carried on as follows : Keep the tool 
continually moistened with soap-suds. Take hold of the tool 
very near to the end, and lean very hard with it on those 
parts which are to be burnished, causing it to glide by a back- 
ward and forward motion without taking it off the piece. 
When it is requisite that the hand should pass over a large 
surface at once without losing its point of support on the work 
bench, be careful in taking hold of the burnisher to place it 
just underneath the little finger. By these means the work is 
done more quickly, and the tool is more solidly fixed in the- 



PREPARATION OF THE METALLIC OBJECTS. 



217 



hand. The burnishers are of various shapes to suit the re- 
quirements of different kinds of work, the first rough burnish- 
ing being often done by instruments with comparatively sharp 
edges, while the finishing operations are accomplished with 
rounded ones. Fig. 105 illustrates the most common forms 
of burnishers of steel and agate. Both must be free from 
cracks and highly polished. To keep them free from blem- 
ishes they are from time to time polished by vigorously rub- 
bing them with fine tin putty, rouge, or calcined alum upon, 

Fig. 105. 




a strip of leather fastened upon a piece of wood which is placed 
in a convenient position upon the work bench. 

Cleansing the -polished objects. — The objects to which high 
luster has been given by means of Vienna lime and oil, or 
rouge, have to be freed from adhering polishing dirt. With 
fiat, smooth objects, this is effected by wiping with a flannel 
rag and Vienna lime, and with those having depressions or 
matted surfaces, by brushing with a soft brush and soap 
water, and then drying in sawdust. 



218 ELECTRO-DEPOSITION OF METALS. 

Cleansing is very much facilitated by brushing the polished 
articles upon a small cloth or flannel bob. 

Chemical Treatment. 

While it is the aim of the mechanical treatment to prepare, 
on the one hand, a pure metallic surface, and on the other, a 
smooth one, the chemical preparation of the objects serves the 
purpose of facilitating the mechanical treatment by softening 
and dissolving the impurities of the surface, and of freeing the 
mechanically treated objects from adhering oil, grease, dirt, 
etc., so as to bring them into the state of absolute purity re- 
quired for the electro-plating process. 

Pickling and dipping. The composition of the pickling 
liquor varies according to the nature of the metal to be 
treated. 

Cast-iron and wrought-iron articles are pickled in a mixture 
of 1 part by weight of sulphuric acid of 66° Be. and 15 parts 
by weight of water.* 

To cleanse badly rusted iron articles without attacking the 
iron itself, it is recommended to pickle them in a concentrated 
solution of chloride of tin, which, however, should not contain 
too much free acid, otherwise the iron is attacked. Bucher 
recommends a pickle composed as follows : Dissolve 3J ozs. 
of chloride of tin in 1 quart of water, and 1 J drachms of tar- 
taric acid in 1 quart of water. Pour the former solution into 
the latter, and add 20 cubic centimeters of indigo solution 
diluted with 2 quarts of water. The object of the addition of 
indigo is not intelligible. 

An excellent pickle for iron is also obtained by mixing 10 
quarts of water with 28 ozs. of concentrated sulphuric acid, dis- 
solving 2 ozs. of zinc in the mixture, and adding. 12 ozs. of 
nitric acid. This mixture makes the iron objects bright, while 
in dilute sulphuric or hydrochloric acid they become black. 

Col. J". H. Hansjosten f recommends the following pickle as 

* The acid should be poured into the water, not the water into the acid. 
t Metal Industry, March, 1913. 



PREPARATION OF THE METALLIC OBJECTS. 219 

giving good results on cast-iron : Sulphuric acid 3 parts, 
hydrofluoric acid 1 part, water 3 to 4 parts. 

" The length of time required to pickle the work in this 
pickle depends on the amount of scale on it, the size of the 
castings, and the strength or weakness of the pickle. Small 
or medium sized castings may be left in it 15 or 20 minutes, 
while larger pieces and pieces with a large, smooth surface, 
should be kept in longer, but the length of time required for 
&ny class of work may be determined by the operator if he 
will watch the results that the first few batches will give. 
He should increase or decrease the strength of the pickle by 
the amount of w r ater or acid needed, and the condition of his 
work demands. After the castings are pickled they should be 
rinsed in hot water containing about \ pound of lime for 
-every 10 gallons of water. The lime water serves a two-fold 
purpose- in that it neutralizes the acid and dries the castings. 
The pickle tank and hot water tank should be side by side and 
covered with a hood made of \ inch boards, high enough 
^.bove the tank so that they will not interfere with the work 
of the operator, but not so high that it will not carry off the 
fumes and steam caused by the acid and lime water. The 
top of the hood should slant downward over the tanks from a 
pipe or stack leading upward, so as to aid the natural draft 
that w T ill carry the steam and fumes away. If the hood ends 
so that the fumes will be guided into a smokestack or chim- 
ney, no exhaust will be necessary, as the natural draft will 
carry them away. 

" Wood boxes, with the nails driven well into the wood and 
of convenient size, with holes bored in the sides and bottom, 
-and iron wires of sufficient strength and long enough so that 
the ends will remain above the solution when attached to the 
box as a handle, make good baskets for small work. Larger 
pieces with holes in them may be strung on iron wire, and the 
■ends looped together, so as to be convenient to take out. 
Pieces of the same kind may be reversed ; that is, put face to 
face or back to back, so that they will not nest and thus pre- 



220 ELECTRO-DEPOSITION OF METALS. 

vent the acid from attacking them all over. Large quantities 
of work may be quickly handled in this way, and, by making 
the tank of proper length, the operator may begin to put in 
work at one end and work toward the other, and by the time 
the tank is rilled the work put in first is nearly ready to come 
out. It is better to have the tank run to size in length rather 
than in breadth or depth. A tank, 30 inches wide, 18 inches 
deep, and 5 or 6 feet long, will be large enough to pickle the 
work for 20 to 30 polishers. Acid should be added to the 
pickle as it weakens, and when it becomes too old it should be 
thrown away and a new one made up. Lime should be 
added to the lime water every day or so. Both solutions 
may be kept in working order for a very long time by simply 
keeping them up to the required strength. No' set rule can 
be laid down to go by in adding acid, or how long the work 
should remain in the pickle. This must be ascertained by the 
operator, and a little experience will quickly tell him what to 
do and when to do it. 

" The scratch-brushing may also be made a factor in turn- 
ing out good work, but is important only in a relative way. 
If it is improperly done, particles of sand ma} r remain in the 
places where the polishing wheel will not reach, and in the 
finished piece will show up as black spots. The cost of 
scratch-brushing is so little, however, that it will be well 
worth while to pay some attention to it, and if the pickling is 
properly done, it is only necessary to brush the loose sand out 
of the background. An objection to pickling that has been 
raised is that the acid will ooze out of the work after plating 
and discolor it. This may occur if the work is pickled too 
much, but a little care will overcome it, or will not allow it to 
happen at all. All time and attention given to this part of 
the preparatory process will be amply repaid, as the result 
cannot be otherwise than a lower cost in polishing." 

For many cases pickling may advantageously be effected in 
the electrolytic way. Suspend the articles in a weak acid 
bath (hydrochloric or sulphuric acid), connect them with the- 



PREPARATION OP THE METALLIC OBJECTS. 221 

positive pole of a source of current, and suspend opposite to 
them a sheet of metal (copper or brass), which is connected 
with the negative pole. 

According to a patent of the Vereinigten Elektrischen 
Gesellschaften, Vienna and Buda-Pest, a 20-per cent, alkaline 
solution of common salt or of Glauber's salt is used for elec- 
trolytic pickling, the metal to be pickled serving as anode. 
By the passage of the current, the electrolyte is broken up into 
sodium-ions, which are separated on the cathodes, and S0 4 
and chlorine-ions, which are separated on the anodes, the 
pickling effect being produced by the latter ions. 

This electrolyte may also be used for freeing sheet metal, 
for instance, sheet-iron, which is to be zincked, from grease, 
and at the same time pickling it. For this purpose the sheet- 
iron is suspended to the anode and object-rods of the bath, and 
a current allowed to enter through the anodes, the sheets 
serving as cathodes being thereby freed from grease by the 
secondarily formed caustic soda. When this has been done, 
the direction of the current is reversed, the former cathodes 
becoming now the anodes, and the former anodes, the cathodes. 
The first having been previously freed from grease are now 
pickled by the separated anions, while the latter are freed from 
grease. When pickling is finished, the sheets which have 
served last as anodes, are taken from the bath and replaced by 
fresh sheets, and the direction of the current having been 
changed, the operation is repeated, a continuous process of 
freeing from grease and pickling being thus possible. With 
about 90 amperes and 4 volts per square meter, pickling, ac- 
cording to the " Metallarbeiter," requires about half an hour. 

To render possible the removal in the electrolytic way of the 
layer of hard solder remaining after soldering bicycle frames 
and thus to allow of perfect enameling, the following method 
is, according to Burgess,* generally adopted in this country. 
The parts to be soldered together were simply dipped in hard 

* Electro-chemical Industry, 1904, No. 1. 



222 ELECTRO-DEPOSITION OF METALS. 

solder whereby a thin layer of hard solder remained upon the 
parts thus treated. To remove this by riling proved expensive, 
and to dissolve by cyanides and solutions of double chromates 
required much time, and was imperfect. With the assistance 
of the electric current and the use of a suitable electrolyte the 
hard solder is completely and rapidly removed without attack- 
ing the steel. A suitable electrolyte for the purpose is a 5-per 
cent, sodium nitrate solution. In consequence of electrolysis 
some sodium nitrate is formed, and this makes the iron or 
steel passive, i. e., deprives it of the power to be attacked by 
the electrolyte, while the hard solder is completely dissolved. 
It must, however, be borne in mind that after several days' 
electrolysis the steel does no longer remain passive, but is per- 
ceptibly attacked^ by the electrolytic pickle, this being due to 
the fact that the electrolyte becomes alkaline and then con- 
tains free ammonia. The latter must therefore be every day 
neutralized by the addition of dilute sulphuric acid. The 
sodium nitrate used for the preparation of the electrolyte- 
should not contain much chloride, as otherwise the iron is 
attacked. 

The correct progress of the operation is recognized by the 
rapid solution of the hard solder, a brown layer remaining 
behind, which can readily be rubbed off. If, however, a thick, 
greenish, firmly adhering slime forms on the anodes, the elec- 
trolyte has become alkaline, and when a brownish foam and 
precipitate appear upon the surface of the electrolyte, the alka- 
linity has become so great that the steel is also attacked. The 
hard solder electrolytically dissolved from the steel frame is 
precipitated as copper and zinc hydroxide by the caustic soda 
secondarily formed on the cathode. This precipitate has from 
time to time to be removed from the bath. The most suitable 
current-densit}" is 0.8 to 1.2 amperes with 3 to 5 volts. 

The duration of pickling depends on the more or less thick 
layer of scale, etc., which is to be removed or softened. The 
process may be considerably assisted and the time shortened 
by frequent scouring with sand or pumice. The pickled 



PREPARATION OF THE METALLIC OBJECTS. 223 

articles are rinsed in cold water, then immersed in hot water, 
and dried in sawdust. In order to neutralize the acid remain- 
ing in the pores, it is advisable to make the rinsing water 
alkaline by the addition of caustic potash or soda, etc. 

Zinc objects are only pickled when they show a thick layer 
of oxide, in which case pickling is also effected in dilute sul- 
phuric or hydrochloric acid, and brushing with fine pumice. 
A very useful pickle for zinc consists of sulphuric acid 100 
parts by weight, nitric acid 100, and common salt 1. The 
zinc objects are immersed in the mixture for one second, and 
then quickly rinsed off in water which should be frequently 
changed. 

Copper, and its alloys brass, bronze, tombac and German silver, 
are cleansed and brightened by dipping in a mixture of nitric 
acid, sulphuric acid, and lampblack, a suitable pickle consist- 
ing of sulphuric acid of 66° Be., 50 parts by weight, nitric acid 
of 36° Be., 100, common salt 1, and lampblack 1. In order 
to remove the brown coating, due to cuprous oxide, the objects 
are first pickled in dilute sulphuric acid, and then dipped for 
a few seconds, with constant agitation, in the above-mentioned 
pickle until they show a bright appearance. They are then 
immediately rinsed in water to check any further action of" 
the pickle. 

If objects of copper or its alloys are not to be subjected, after 
pickling, to further mechanical treatment, or are to be at once 
placed in the electro-plating bath, it is best to execute the 
pickling process in two operations by treating them in a pre- 
liminary pickle and brightening them in the bright- dipping 
bath. The preliminary pickle consists of nitric acid of 36° Be., 
200 parts by weight, common salt 1, lampblack 2. In this 
preliminary pickle the articles are allowed to remain until all 
impurities are removed, when they are rinsed in a large 
volume of water, dipped in boiling water, so that they quickly 
dry, and plunged into the bright-dipping bath, which consists 
of nitric acid of 40° Be., 75 parts by weight, sulphuric acid of 
66° Be., 100, and common salt 1. It is not' advisable to bring 



"224 ELECTRO-DEPOSTTION OF METALS. 

the objects which have passed through the preliminary pickle 
-and rinsing water directly, while still moist, into the bright- 
dipping bath, since for the production of a beautiful, pure 
luster the introduction of water into the bright-dipping bath 
must be absolutely avoided. 

Hence the objects treated in the preliminary pickle should 
first be dried by heating in hot water, shaking the latter off. 

Potassium cyanide, dissolved in ten times its weight of 
water, is often used instead of the acid pickle for brass, es- 
pecially when it is essential that the original polish upon the 
objects should not be destroyed, as in the preparation of 
articles for nickel-plating. The objects should remain in this 
liquid longer than in the acid pickle, because the metallic 
•oxides are far less soluble in this than in the latter. In all 
<3ases the final cleaning in water must be observed. 

All acid pickles used for different kinds of work should be 
kept distinct from each other, so that one metal may not be 
dipped into a solution containing a more electro-negative 
metal, which would deposit upon it by chemical exchange. 

The pickled objects must not be unnecessarily exposed to 
the air, and should be transferred as quickly as possible from 
the pickle to the wash-waters, and then to the electro-plating 
bath, or, if this is not feasible, kept under pure water. Pickled 
objects which are not to be plated are carefully washed in 
water, which should be frequently changed, then rinsed, 
drawn through a solution of tartar, and dried by dipping in 
hot water and rubbing with sawdust. 

Places soldered with soft solder, as well as parts of iron, 
become black by pickling, and have to be brightened by 
•scouring with pumice, or by scratch-brushing. 

Mat-dipping. Objects of brass or other alloys of copper 
are frequently to be given a dead surface so that after plating 
they show a beautiful mat luster. Very fine effects may by 
this means be obtained, especially in the bronze-ware industry. 
Matting may be effected in various ways. Every bright dip 
■acts as a mat dip if the objects are exposed to its effect for a 



PREPARATION OF THE METALLIC OBJECTS. 225 

longer time and at a higher, temperature. Matting is, how- 
ever, made more effective by adding zinc sulphate to the dip, 
the matting being the more pronounced, the more zinc sul- 
phate has been added. 

A good mat dip is prepared by pouring a solution of 0.35 
oz. of zinc sulphate in 3 J ozs. of water in a cold mixture of 
6J lbs. of nitric acid of 36° Be., 4.4 lbs. of sulphuric acid of 
'66° Be., and % oz. of common salt. According to the shade 
of mat desired, the objects are allowed to remain in the dip 
for 2 to 10 minutes. The objects, which on coming from the 
mat-dip show a faded, earthy appearance, are rapidly drawn 
through a clean bright dip, whereby they acquire the mat 
luster, and are then quickly rinsed in a large volume of water. 

For the production of a mat-grained surface by pickling, 
the following mixture may be recommended : Saturated solu- 
tion of potassium dichromate 1 part by volume, and concen- 
trated hydrochloric acid 2 parts by volume. In this mixture 
the brass articles are allowed to remain several hours. They 
are then rapidly drawn through the bright-dipping bath and 
rinsed in a larger volume of water frequently renewed. 

A delicate matted surface may be produced by electrolytic 
pickling or etching. The process is the same as described 
above under iron. 

Other methods of matting will be given under "Gilding." 

Generally speaking, it may be said that less depends on the 
composition of the pickle than on quick and skilful manipula- 
tion ; and as good results have always been obtained with the 
above-mentioned mixture, there is no reason for repeating the 
innumerable receipts given for pickles. The main points are to 
have the acid mixture as free from water as possible, further to 
develop hyponitric acid which is effected by the reduction of 
nitric acid in consequence of the addition of organic substances 
(lampblack, sawdust, etc.), and of chlorine, which is formed by 
the action of the sulphuric acid upon the common salt. The 
volume of the dipping bath should not be too small, since in 
pickling the acid mixture becomes heated and the increased 
15 



226 



ELECTRO-DEPOSITION OF METALS. 



temperature shows a very rapid, frequently not controllable, 
action, so that a corrosion of small articles may readily take 
place. It is therefore necessary to allow the acid mixture, 
after its preparation, to thoroughly cool off. Pour the sul- 
phuric acid into the nitric acid (never the reverse/) and allow 
the mixture, which thereby becomes strongly heated, to cool 
off to at least the ordinary temperature. 

In order to be sure of the uniform action of the pickle upon 
all parts, it is, in all cases, advisable previous to pickling to 

Fig. 106. 




free the articles from grease by one of the methods given 
later on. 

In pickling abundant vapors are evolved which have an in- 
jurious effect upon the health of the workmen, and corrode 
metallic articles exposed to them. The operation should, 
therefore, be conducted in the open air, or under a well- 
drawing vapor-flue. 

In large establishments it may happen that the quantity of 
escaping acid vapors is so large as to become a nuisance to the 
neighborhood, which the proprietors may be ordered by the 



PREPARATION OF THE METALLIC OBJECTS. 227 

authorities to abate. The evil is best remedied by a small 
absorbing plant, as follows : 

Connect the highest point of the vapor-flue D (Fig. 106) by 
a wide clay pipe R with a brick reservoir, A, laid in cement, 
so that R enters A a few centimeters above the level of the 
fluid, kept constantly at the same height by the discharge pipe 
b. Above, the reservoir is closed by an arch through which 
the water conduit IF is introduced. Below the sieve S, which 
is made of wood and coated with lacquer, a wide clay pipe R 
leads to the chimney of the steam boiler ; or the suction pipe 
of an injector is introduced in this place, into which the air 
from the vapor-flue is sucked through the reservoir and 
allowed to escape into the open air or into a chimney. 
Through the man-hole if, the sieve-bottom S of the reservoir 
is filled with large pieces of chalk or limestone. The manner 
of operating is now as follows : A thin jet of water falls upon 
S, where it is distributed and runs over the layer of chalk. 
The air of the pickling room saturated with acid vapor moves 
upward in consequence of the draught of the chimney of the 
steam boiler, the injector, or the ventilator, and yields its con- 
tent of acid to the layer of chalk, while the neutral solution 
of calcium nitrate and calcium chloride, which is thus formed, 
runs off through b. 

The absorption of the acid vapors may, of course, be effected 
by apparatus of different construction, but the one above de- 
scribed may be recommended as being simple, cheap, and 
effective. 

The considerable consumption of acid for pickling purposes 
in large establishments makes it desirable to regain the acid 
and metal contained in the exhausted dipping baths. The 
following process has proved very successful for this purpose : 
Mix the old dipping baths with £ their volume of concentrated 
sulphuric acid, and bring the mixture into a nitric acid distill- 
ing apparatus. Distil the nitric acid off at a moderate temper- 
ature, condense it in cooled clay coils, and collect it in glass 
balloons. To the residue in the still add water, precipitate 



228 ELECTRO-DEPOSITION OF METALS. 

from the blue solution, which contains sulphate of copper and 
zinc, the copper with zinc waste, and add zinc until evolution 
of hydrogen no longer takes place. Filter off the precipitated 
copper through a linen bag, wash, and dry. The fluid run- 
ning off, which contains zinc sulphate, is evaporated to crystal- 
lization and yields quite pure zinc sulphate, which may be 
sold to dye-works, or for the manufacture of zinc-white. 

According to local conditions, for instance, if the zinc sul- 
phate cannot be profitably sold in the neighborhood, or zinc 
waste cannot be obtained, it may be more advantageous to omit 
the regaining of zinc from the dipping baths. In this case the 
fluid which is obtained by mixing the contents of the still with 
water is compounded with milk of lime until it shows a slightly 
acid reaction. The gypsum formed is allowed to settle, and 
after bringing the supernatant clear fluid into another reservoir, 
the copper is precipitated by the introduction of old iron. The 
first rinsing waters in which the pickled objects are washed 
are treated in the same manner. The precipitated copper is 
washed and dried. 

Removal of grease and cleansing. These two operations must 
be executed with most painstaking exactness because on them 
chiefly depends the success of the electro-plating process. 
Their object is to remove every trace of impurity, be it due to 
the touching with the hands or to the manipulation in grind- 
ing and polishing, and to get rid of the layer of oxide which 
is formed in removing the grease with lyes and other agents. 

According to the preparatory treatment of the articles, the 
removal of grease is a more or less complicated operation. 
Large quantities of oily or greasy matter should be removed 
by washing with benzine or petroleum, it being advisable to 
execute this operation immediately after grinding and polish- 
ing, so that the oil used in these operations has no chance of 
hardening, as is frequently the case with articles preparatively 
polished with Vienna lime and stearine oil. Instead of clean- 
ing with benzine or petroleum, the articles, as far as their 
nature allows, may be boiled in a hot lye consisting of 1 part 



PKEPAEATION OF THE METALLIC OBJECTS. 229 

of caustic potash or soda in 10 of water, until all the grease is 
saponified, when the dirt, consisting of grinding powder, can be 
readily removed by brushing. In place of solution of caustic 
alkalies, hot solution of soda or potash may be used, but its 
action is much slower and offers no advantages. Objects of 
tin, lead and Britannia must be left in contact with the lye 
for a short time only, as otherwise they are attacked by it. 

The articles thus freed from the larger portion of grease are 
first rinsed in water, and then, for the removal of the last traces 
of grease, are brushed with a bristle brush and a mixture of 
water, quicklime and whiting until, when rinsed in water, all 
portions appear equally moistened and no dry spots are visible. 

The lime mixture or paste is prepared by slaking freshly- 
burnt lime, free from sand, with water to an impalpable pow- 
der, mixing 1 part of this with 1 part of fine whiting, and 
adding water, stirring constantly, until a paste of the con- 
sistency of syrup is formed. 

The shape of many objects presents certain difficulties in the 
removal of grease, as the deeper portions cannot be reached 
with the brush, as, for instance, in skates, which often are to 
be nickeled in a finished state. In this case the objects are 
drawn in succession through three different benzine vessels. 
In the first benzine most of the grease is dissolved, the rest in 
the second, while the third serves for rinsing off. When the 
benzine in the first vessel contains too much grease, it is emp- 
tied and filled with fresh benzine, and then serves as the third 
vessel, while that which was formerly the second becomes the 
first, and the third the second. After rinsing in the third ben- 
zine vessel, the objects are plunged in hot water, then for a few 
seconds dipped in thin milk of lime, and finally thoroughly 
rinsed in water. It is recommended not to omit the treatment 
with milk of lime of objects freed from grease with benzine. 

Electro-chemical cleaning. It has been found that alkaline 
substances, such as sodium carbonate, potassium carbonate, 
potassium hydroxide and sodium hydroxide in solution, in 
varying degrees of concentration and with small proportions of 



230 ELECTRO-DEPOSITION OF METALS. 

potassium cyanide added, will with a sufficiently strong electric 
current of from 4 to 8 volts, and at a temperature nearly boil- 
ing, develop sufficient hydrogen to remove entirely all organic 
substances from the surface of the metal, thereby leaving it 
chemically clean. 

This method has brought into the market several new com- 
binations which are sold under the name of electro-chemical 
cleaning salts, and have given very satisfactory results. 

In a paper read at the convention of the American Brass 
Founders' Association, at Toronto, Canada, 1908, Charles H. 
Proctor, in speaking of electro-chemical cleaning baths and 
their application, says : * 

" The action of an electro-cleanser is similar to the action of 
an electro-plating bath. The only difference as far as the de- 
velopment of gases is concerned, is that no metal being in 
solution and the anode being insoluble, no metal is deposited. 
But with a strong current a copious evolution of oxyhydrogen 
gas is developed upon the articles, which attacks the organic 
matter upon the surface, practically lifting it off and by rapid 
evolution of the gases carries it to the surface. The small 
quantity of potassium cyanide contained in solution absorbs 
the slight oxidation that might be upon the surface, and by 
the combined action produces a surface clean enough, after 
washing in clear water, for any deposits. 

" The arrangement of an electro-cleaning bath is very 
simple. Prepare a wrought-iron tank of proportions best 
adapted to the amount of work to be cleansed. This should 
"be heated with steam coils of iron. Across the top of the 
tank an insulated frame should be constructed. Upon this 
frame place three conducting poles, as on the regular plating 
bath. To the two outside poles the positive current should 
be carried direct. This can best be accomplished with at 
least J-inch copper-wire flexible cables. To the center pole 
the negative current is connected with cables of the same 

*The Metal Industry, June, 1908. 



PREPARATION OF THE METALLIC OBJECTS. 231 

dimensions ; no rheostats are necessary. The stronger the 
current the greater the evolution of gases and the quicker the 
cleansing operation is accomplished. 

" Although direct contact can be made with the positive 
current to the tank itself, in practice better results have been 
obtained with anodes of sheet-iron not more than 6 inches 
wide and of a length in proportion to the depth of the tank. 

" The electro-cleaning solution should consist (for ordinary 
purposes) of 3 to 4 ozs. caustic potash to each gallon of water, 
and to every 100 gallons of solution 8 ozs. cyanide of potas- 
sium. This can be varied according to conditions. It is ad- 
visable to add at least I lb. cyanide each week. Where the 
articles, such as iron or steel, contain much oil or grease upon 
the surface, the density of the solution can be increased. For 
articles of brass, copper or bronze that have been polished, 
use a solution of carbonate of soda in the proportion of 2 ozs. 
soda and J oz. caustic potash to each gallon of water, with 
the addition of 4 ozs. of cyanide to every 100 gallons of solu- 
tion. If much organic matter is upon the surface of the 
articles to be cleansed, it is advisable where an air pressure 
can be obtained from an ordinary blower, to arrange a pipe so 
that the current of air can be deflected upon the surface of the 
solution, thus keeping the center of the solution clear of the 
insoluble substances that arise to the surface. When the 
cleanser is at rest, as much of this matter should be removed 
as possible. 

"It should be the aim of the operator to use the same 
methods of avoiding all unnecessary contamination as he 
would in electro-depositing baths. It is obvious even to those 
who have not practiced this method of cleansing metallic 
articles that large quantities of work can be treated very 
rapidly, and this is the case especially where frames or racks 
are used in the plating operations. On account of the rapidity 
of operation and the efficiency of the bath, this method of 
cleansing should be a part of the labor-saving devices used in 
all great commercial establishments engaged in the electro- 
plating of metals." 



232 



ELECTRO-DEPOSITION OF METALS. 



To avoid subsequent touching with the hands the objects,, 
before freeing them from grease, must of course be tied to the 
metallic wires (of soft copper) by which they are suspended in 
the electro-plating bath. In removing the grease by the wet 
method a layer of oxide scarcely perceptible to the eye is fre- 
quently formed upon the metals. This layer of oxide has to 
be removed, the liquid used for the purpose varying, of course, 
with the nature of the layer. 



Fig. 107. 



Fig. 108. 





Objects of iron and steel, as well as of zinc, are momentarily 
plunged in a mixture of sulphuric acid 1 part by weight and 
water 20 parts, and quickly rinsed off in clean water. Highly 
polished objects of iron and steel, after being treated with this 
mixture, are best again rapidly brushed with lime paste, and, 
after rinsing off quickly, immediately brought into the electro- 
plating bath. 

Copper, brass, bronze, German silver, and tombac are best. 



PKEPARATION OF THE METALLIC OBJECTS. 233 

cleaned with a dilute solution of potassium cyanide, 1 part of 
60-per cent, potassium cyanide in 15 to 20 of water. The 
objects are then quickly rinsed off and placed in the electro- 
plating bath. 

Lead and Britannia may be treated with water slightly 
acidulated with nitric acid. 

The difficult and dangerous operation of tilting heavy carboys 
containing acid is- overcome by the use of the Hanson & Van 
Winkle acid pump shown in Figs. 107 and 108. In using this 
pump it is not necessary for two men to handle a carboy. A 
workman carries the acid pitcher or receptacle to the carboy; 
one end of the pump tube is placed in the acid, the rubber- 
cork making an air-tight joint in the neck of the carboy, and 
the other end of the pump is carried to the pitcher. On 
pumping a steady flow of acid is obtained. 

Electro-plating Solutions [Electrolytes, Baths). 

Next to the proper mechanical' and chemical preparations 
of the objects, the success of the process of electro-deposition 
depends on the suitable composition of the electro-plating 
solutions, electrolytes, or baths, and the proper current-strength 
which is conducted into the baths for the precipitation of the 
metals. In regard to the latter the most essential conditions 
have already been discussed in Chap. IV., "Electro-plating 
Plants in General," and will be further referred to in speaking 
of the several electro-plating processes. Hence, the general 
rules which have to be observed in the preparation of the 
baths will first be considered. 

Solvents. — With the exception of the baths prepared with 
glycerin according to the patent of Marino, water is the solvent 
used in the preparation of all baths, and its constitution is by 
no means of such slight importance as is frequently supposed. 

Spring and well waters often contain considerable quantities 
of lime, magnesia, common salt, iron, etc., the presence of 
which may cause various kinds of separations in the baths. 
On the other hand, river water is frequently impregnated to 



234 ELECTRO-DEPOSITION OP METALS. 

such an extent with organic substances that its employment 
without previous purification cannot be recommended. No 
doubt, distilled water, or in want of that rain water, is the 
most suitable for the preparation of baths. However, rain 
water collected from metal roofs should not be used, nor that 
running off from other roofs, it being contaminated with dust. 
When used, it should be caught in vessels of glass, earthen- 
ware, or wood, free from tannin, and filtered. Where river or 
well water has to be employed, thorough boiling and filtering 
before use are absolutely necessary in order to separate the 
carbonates of the alkaline earths held in solution. By boiling, 
a possible content of sulphuretted hydrogen is also driven off. 

Purity of chemicals. Another important factor is the purity 
of the chemicals used for the baths, the premature failure of 
the latter being in most cases caused by the unsuitable nature 
of the chemicals, which also frequently gives rise to abnormal 
phenomena inexplicable to the operator. Chloride of zinc, for 
instance, may serve as an example. It is found in commerce 
an Very varying qualities, it being prepared for dyeing pur- 
poses with about 70 per cent, actual content of chloride of 
zinc, for pharmaceutical purposes with about 90 per cent., and 
for electro-plating purposes with 98 or 99 per cent. Now it 
will readily be seen that if an operator who is preparing a 
brass bath according to a formula which calls for pure chloride 
•of zinc uses a preparation intended for dyeing purposes, there 
will be a deficiency of metallic zinc in the bath, and the con- 
tent of copper in the bath being too large in proportion to the 
zinc present, will cause reddish shades in the deposit. 

Likewise, in case the operator uses potassium cyanide of low 
content, when the formula calls for a pure article with 98 per 
cent., he will not be able to effect the solution of copper or 
zinc salts with the quantity prescribed. Furthermore, potas- 
sium cyanide, in the preparation of which prussiate of potash 
containing potassium sulphate is used, will cause, by reason of 
the formation of potassium sulpho-cyanide, various disturbing 
influences (formation of bubbles in the deposit), the explana- 



PREPARATION OP THE METALLIC OBJECTS. 235 

tioh of which is difficult to the operator, who, trusting to the 
purity of the chemicals, seeks elsewhere for the causes of the 
abnormal phenomena. 

Sodium sulphite may in similar manner cause great annoy - 
-ance if the suitable preparation is not used. There is a crystal- 
ized neutral salt which is employed for many gold baths, and 
&lso the bisulphite of soda in the form of powder which serves 
for the preparation of copper and brass baths. If the latter 
should be used in the preparation of gold baths, the gold 
would be reduced from the solution of its salts and precipitated 
as a brown powder. 

Or, if in preparing nickel baths, a salt containing copper is 
used, the nickeling will never be of a pure white color, but 
show shades having not even a distant resemblance to the 
•color of nickel. 

The above-mentioned examples will suffice to show how 
careful the operator must be in the selection of the sources 
from which he obtains his supplies. It may be here men- 
tioned that all the directions given in the following pages 
refer to chemically pure products ; where products of a lower 
standard may be used their strength is especially given. 

Concentration of baths. — For the concentration of the various 
baths no general rules can be laid down ; neither can the de- 
termination of the density of the baths by the hydrometer be 
relied on. If electro-plating solutions consisted of nothing 
but the pure metallic salts, the specific gravity, which is indi- 
cated by the hydrometer-degrees, might serve for an estimation 
of their value. But such an estimation is often apt to prove 
deceptive, since, to decrease the resistance, the baths also re- 
quire conducting salts, and by the addition of a larger quantity 
of them, the specific gravity of a bath may be increased to 
any extent without the content of the more valuable metal 
being greater than in a bath showing fewer hydrometer-degrees. 

When the operator is acquainted with the composition of 
the baths, and knows how many degrees Be. a fresh bath 
should show when correctly prepared, he can draw a con- 



236 ELECTRO-DEPOSITION OF METALS. 

elusion as to the condition of the bath by changes in the- 
specific gravity. If, for instance, a nickel bath when freshly 
prepared shows the standard specific gravity — 70° Be. — for 
nickel baths, and it shows later on 90° Be., the greater spe- 
cific gravity is due either to evaporation of water or to excessive 
refreshing or strengthening of the bath. Such a bath gen- 
erally yields dark or spotted nickeling, the deposit is formed 
in a sluggish manner, and readily scales off with a stronger 
current. The operator in this case may recognize from the 
hydrometer that the cause of these phenomena is not due to a 
contamination of the bath, but to its over-concentration. 
Baths, when too concentrated, readily deposit salts in crystals 
on the anodes and the sides of the tanks, which should by no 
means take place, and there is even danger of microscopic 
crystals depositing upon the articles and causing holes in the 
deposit. 

A plating bath should never be poor in metal, as otherwise 
it soon becomes exhausted, and besides the deposits form more 
slowly and with less density than in baths with a correct con- 
tent of metal. 

Hence in summer when the temperature of the bath, is 
naturally higher, they can be made more concentrated than in 
winter. If crystals are separated, even when a bath shows a 
temperature of 58° F., they should be removed and dissolved 
in hot water. The solution is returned to the bath and water 
is added to the latter until the formation of crystals ceases. 

Agitation of the baths. — In order that all the strata of the 
bath may show an equal content of metal, it is advisable in 
the evening, after the day's work is done, to thoroughly stir 
up the solution with a wooden crutch. For practical reasons 
the baths are generally made one-quarter to one-third deeper 
than corresponds to the lengths of the objects io be plated. In 
consequence of this, the strata of fluid between the anodes and 
the objects become poorer in metal than those on the bottom, 
and the object of stirring up is to restore the same concentra- 
tion to all portions of the bath. 



PREPARATION OF THE METALLIC OBJECTS. 237 

While stirring up the bath, it is also advisable to see whether 
any metallic articles have become detached from the slings 
and dropped to the bottom of the vat. Such articles must be 
"taken out, since they are dissolved by some baths, the latter 
being thereby spoiled. This examination must be especially 
thorough with nickel baths. 

The strata of fluid which come in contact with the anodes 
become, by the absorption of metal, specifically heavier than 
the other strata and sink to the bottom of the tank, while, on 
the other hand, the strata of fluid which yield metal to the 
articles become specifically lighter and rise to the top. A 
partial compensation, of course, takes place by diffusion, but 
not a complete one, and from this cause arise several annoy- 
ances. The heavier and more saturated fluid offering greater 
resistance to the current, the anodes are attacked chiefly on 
the upper portions where the specifically lighter 
layer of fluid is; practically this is proved by the 
appearance of the anodes, which, at first square, 
after being for some time used, assume the shape 
shown in Fig. 109. 

On the other hand, the portions of the cathodes 
(objects) which come in contact, near the surface, 
with strata of fluid poor in metal, acquire a deposit |l§|| 
of less thickness than the lower portions which dip 
into the bath where it is richer in metal. Now if 
the bath also contains free acid, and if there is a considerable 
difference in the specific gravity of the lower and upper strata 
of fluid, the electrode, which touches both strata, produces a 
current, the effect of which is that metal dissolves from the 
upper portions and deposits upon the lower. This explains 
the phenomenon that a deposit on the upper portions of the 
objects may be redissolved, even when a current, which, how- 
ever, must be very weak, is conducted into the bath from an 
external source. 

Many authors, therefore, go so far as to demand that during 
the electro-plating process the baths should be kept in con- 




238 ELECTRO-DEPOSITION OF METALS. 

stant agitation by mechanical means. This, however, is- 
scarcely necessary, because a homogeneity of the solution is 
to a certain extent effected by the agitation of the fluid in 
suspending and taking out the objects. Hence as long as 
objects are put in and taken out, an agitation naturally takes 
place in which all the strata of fluid between the objects and 
anodes take part, while only the deepest strata, which do not 
come into contact with the objects and the anodes, remain in 
a state of stagnation. 

Constant agitation of the plating solution is of advantage in 
silvering, and in galvanoplastic reproduction in the acid copper 
bath, in which the articles have to remain four to five, and eight 
to ten hours. With constant agitation of the bath it is possi- 
ble to work with a greater electro-motive force, whereby the 
deposits are finished in a shorter time ; and in silvering, the 
formation of current-streaks is, to a certain extent, avoided ;. 
and in galvanoplastic reproduction, the formation of so-called 
blooms. In nickeling, with constant agitation of the bath, 
heavier deposits can, without doubt, be obtained in a shorter 
time and without premature deadening of the deposit. 
. Henry Sand * draws attention to the fact that, according to- 
all known experience, the greater current-densities which are 
permissible in the electrolysis of given metal salt solutions, de- 
pend solely on the rapidity of the renewal of the fluid on the 
electrode. In his opinion it is very probable that, in the depo- 
sition of metals, the cathode potential in itself is independent 
of the current-density, further that the quality of the metal 
deposits is but slightly influenced by the current-density, and 
that the greater variations in the nature of the deposits with 
different current-densities is almost exclusively due to local 
changes in concentration. 

These changes in concentration — the impoverishment in 
metal ions of the electrolyte on the place where it comes in 
contact with the cathode — is according to Daneel f caused, on 

* Zeitschrift fur Elektrochemie, 1904, S. 452. 
t Zeitschrift fur Elektrochemie, IX, 763. 



PREPARATION OF THE METALLIC OBJECTS. 239 

the one hand, by the separation of metal ions on the cathode ; 
further, in complex salt solutions, by the accumulation of ions 
of the salt which with the metal salt forms the complex com- 
bination, and by the conveyance by the current of the metal 
in those complex salt solutions which form complex anions 
containing the metal to be separated, and migrate away from 
the cathode to the anode. 

The impoverishment in metal ions would proceed still more 
rapidly but for the counter-action of certain forces. First of 
all, diffusion has to be taken into consideration ; it causes the 
entrance of strata of fluid richer in metal into those poorer in 
metal, and it is greatest on the sides where impoverishment has 
progressed furthest. Further, fresh ions are constantly sup- 
plied by dissociation, and by solutions of the simple as well as 
the complex salts which contain the metal in the cation, 
impoverishment is counteracted by the conveyance of metal 
by the current. 

When working with low current-densities in an electrolyte, 
even when the latter is at rest, the slighter concentration of 
ions appearing on the cathode is to a certain extent obviated 
by diffusion of fluid richer in metal ; hence under such condi- 
tions good deposits are obtained without agitation of the elec- 
trolyte. 

The case, however, is different when in the same electrolyte- 
depositions are made with high current-densities, serviceable 
deposits being only obtained so long as sufficient concentration 
of metal ions is present on the points of contact of the electro- 
lyte with the cathode. However, as diffusion is no longer 
sufficiently great to replace the content of metal separated, 
hydrogen ions are next separated, together with the metal 
ions supplied by diffusion, which causes, almost without ex- 
ception, the formation of spongy deposits. Hence in rapid 
electrolysis for which high current-densities are employed, the 
local exhaustion of the layers on the cathode has to be pre- 
vented by vigorous agitation of the electrolyte. 

Constant agitation effects also the more rapid removal of 



240 ELECTRO-DEPOSITION OF METALS. 

the hydrogen-bubbles which form on the articles, but the same 
end is attained without complicated contrivances by the oper- 
ator accustoming himself to strike the object-rod a slight blow 
with the finger each time he suspends an object. 

Temperature of the baths. The temperature required for the 
electro-plating solutions has already been referred to on p. 
120, where also the means have been given for bringing baths 
which have cooled down too much to the proper degree of 
temperature. Baths which are to be used cold should under 
no circumstances show a temperature below 59° F., it being 
best to maintain them at between 64.5° and 68° F. 

The warmer a bath is, the less its specific resistance and the 
greater its conducting power, because the salts dissolved in the 
bath are more dissociated than when the electrolyte is cold. 
In warm solutions the hydrogen-bubbles separated by the 
cathodes escape much more rapidly than in cold electrolytes, 
and consequently there is less chance of hydrogen occlusion 
which, according to general opinion, is the principal cause of 
the deposit peeling off. 

Boiling the baths. — Boiling is required in the preparation of 
many baths, if, after cooling, they are to yield good and cer- 
tain results. The kettles and boiling-pans used for the purpose 
are of various shapes, hemispherical or with flat bottom, and 
are made of different materials, those of enameled iron, or, 
for small baths, of porcelain or earthenware, being best. The 
enamel of the iron kettles must be of a composition which is 
not attacked by the bath. Notwithstanding their enamel these 
vessels become gradually impregnated with the solutions they 
have held, and it is risky to employ them for different kinds 
of baths. Thus, an enameled kettle which has been used for 
silvering will not be suitable, even after the most thorough 
washing, for a gold bath, as the gilding will certainly be white 
or green, according to the quantity of silver retained by the 
vessel. The use of metal vessels should be avoided. Copper 
and brass baths may, however, be boiled in strong copper 
^kettles, though they are somewhat attacked. A copper kettle, 



PREPARATION OF THE METALLIC OBJECTS. 241 

after being freed from grease and scoured bright, may be pro- 
vided with a thick deposit of nickel by filling it with a nickel 
bath, connecting it with the negative pole of a strong battery 
or dynamo machine, and suspending it in a number of nickel 
anodes connected with the positive pole. Such nickeled kettles 
may be used for boiling nickel baths, but enameled kettles or 
large dishes of nickel-sheet, or vessels lined with lead, deserve 
the preference. Generally speaking, nickel baths do not re- 
quire actual boiling, but the nickel salts and certain conduct- 
ing salts which constitute the baths, dissolve with difficulty 
in cold water, and hence solution is effected in hot water. 

When, for the preparation of nickel baths, nickel salts soluble 
with difficulty have to be dissolved with the assistance of heat, 
and no suitable vessel is available for the purpose, solution 
may be effected as follows : Bring pure water in a bright cop- 
per kettle to the boiling-point. Pour the hot water into a 
clean wooden bucket holding from 8 to 10 quarts, and add the 
quantity of nickel salt corresponding to the quantity of water. 
Stir with a wooden crutch until solution is complete. Repeat 
the operation until all the salt required is dissolved. 

For very large baths this process would, however, require 
too much time, and it is, therefore, advisable to use a large 
round or oval wooden tank, or a tank lined with pure sheet 
lead. The contents of the tank are heated by means of a lead 
coil through which steam is introduced. 

Working the baths with the current. In case boiling of large 
quantities of fluid is not feasible, the same object may be at- 
tained by working the bath for some time with the electric cur- 
rent. The anode rods are hung full of anodes and, a few plates 
of the same kind of metal having been secured to the object- 
rods, a current of medium strength is conducted into the bath 
until an object, from time to time suspended in the bath, is 
properly covered with a deposit. This process is frequently 
used with great success for large brass baths. 

Objections have been made to the process because it is some- 
times carried too far, the solution becoming thereby demetal- 
16 



242 ELECTRO-DEPOSITION OF METALS. 

lized (?). However, there is no reason for objecting to a pro- 
cess because some operators carry it out in a bungling manner, 
and in our opinion a bath which cannot stand working for 
several days with the current without becoming poor in metal 
is not of the proper composition. 

Filtering the baths. Should the solutions after their prepa- 
ration, and, if necessary, boiling, not be perfectly clear, they 
have to be filtered. For large baths this is best effected by 
means of felt filter bags, and for smaller baths, especially those 
of the noble metals, with filtering paper. This removal of 
the particles held in suspension is necessary to prevent their 
deposition upon the objects, which might cause small holes in 
the deposit, as well as roughness and other defects. It is still 
better to allow the baths to clarify by standing quietly, and 
to draw off the clear solution bj r means of a siphon. The 
turbid residue is then filtered. 

Prevention of impurities. To secure lasting qualities to the 
baths they must be carefully protected from every possible 
contamination. When not in use for plating they should be 
covered to keep out dust. The objects before being placed in 
the baths should be free from adhering scouring material or 
dipping fluid, which otherwise might, in time, spoil the bath. 
The cleansing of the anode and object rods by means of sand- 
paper, or emery-paper, should never be done over the bath, 
so as to avoid the danger of the latter being contaminated by 
the oxides of the metal constituting the rods falling into it. 
When a visible layer of dust has collected upon the bath, it 
must be removed, as otherwise particles of dust might deposit 
upon the objects and prevent an intimate union of the deposit 
with the basis-metal. With large baths the removal of the 
layer of dust is readily effected by drawing a large piece of 
filtering or tissue paper over the surface, and repeating the 
operation with fresh sheets of clean paper until all the dust is 
removed. Small baths should be filtered. 

Tfie choice of anodes is also an important factor for keeping 
the baths in good condition, as well as for obtaining good 



PREPARATION OP THE METALLIC OBJECTS. 243 

results. The anodes should always consist of the metal which 
is deposited from the solution; and the metal used for them 
must be pure and free from all admixtures. To replace as 
much as possible the metal withdrawn from the bath by the 
electro-plating process, the anodes must be soluble; and it is 
wrong if, for instance, nickel baths are charged with insoluble 
anodes of carbon; or for smaller baths, of sheet platinum, 
provided the chemical composition of the bath does not in 
part demand insoluble anodes. Insoluble anodes cause a 
steady and rapid declination in the content of metal, an ex- 
cessive formation of acid in the bath, and, by the detachment 
of particles of carbon, a contamination of the solution. 
Further particulars in regard to anodes will be given in dis- 
cussing the separate baths. 

Absorption of the deposit. When upon a pure metallic sur- 
face another metal is electro-deposited, the first portion of the 
deposit penetrates into the basis-metal, thus forming an alloy. 
This may be readily proved by repeating Gore's experiments. 
If a thick layer of copper be precipitated upon a platinum 
sheet, and then heated to a dark-red heat, the deposit can be 
entirely peeled off. By then heating the platinum sheet with 
nitric acid, and thoroughly washing with water, it appears, 
after drying, entirely white and pure. By reheating the sheet, 
the surface becomes again blackened by cupric oxide, and by 
frequently repeating the same operation, a fresh film of cupric 
oxide will always be obtained. 

This penetration of the deposit into the basis-metal, how- 
ever, does not merely take place during electro-plating, but 
also later on ; and it may frequently be observed that, for in- 
stance, zinc objects only slightly coppered or brassed, after 
some time become again white. Since this also happens when 
the deposits are protected by a coat of lacquer against atmos- 
pheric influences, the only explanation of the phenomenon 
can be that the deposit is absorbed by the basis-metal, w T hich 
is also confirmed by analysis. This fact must be taken into 
consideration if durable deposits are to be produced. 



244 ELECTRO-DEPOSITION OF METALS. 

Effect of the current-density. A greater or smaller current- 
density used in operating is not without influence upon the 
electrolytes. The greater the current-density is, the more 
metal will be deposited on the cathode, while on the anode 
the oxidation of the metal and its solution into acid residues 
cannot take place in the same measure, the result being 
further decompositions, oxygen gas being liberated. In con- 
sequence of this there appear also greater differences in con- 
centration than when depositing with less current-density and, 
as regards concentration, the electrolyte will remain most 
constant when working with a smaller current-density. 

For depositions upon strongly profiled objects a medium 
current-strength will prove most suitable. Daneel * pictures 
the process as follows : If a deposit is made upon an article 
with elevations and depressions, the current lines will crowd 
together towards the elevated points, i. e., those nearer to the 
anodes, since the current always chooses the most convenient 
way. Now owing to the deposit an impoverishment in metal 
in the electrolyte takes place on the elevated portions, and the 
consequence is that on these portions the separation-tension is 
increased. However, when the latter is increased the current- 
lines will turn towards more favorable portions richer in metal 
ions, i. e., those lying deeper, until an impoverishment in metal 
ions there also takes place. From this it follows that with a 
medium current-strength the current-lines cannot permanently 
favor any particular portions of the cathodes, and the deposit 
must become uniform. Should an unequal impoverishment 
take place on the electrode it would be overcome by short- 
closed circuits formed there, which means that they cannot 
distribute themselves unequally over the surface of the cathode. 

With very small current-densities the process would be dif- 
ferent. When the current-density is so small that an im- 
poverishment in metal ions on the entire electrode can be 
prevented by diffusion, the current-lines will permanently 

* Zeitschrift fur Elektrochemie, IX, 763. 



PREPARATION OP THE METALLIC OBJECTS. 245 

crowd together upon the more elevated portions, and the 
deposit will grow there, while less metal deposits in the 
depressions. 

In practice it has been found that a great distance of the 
anodes from the profiled cathodes, thorough agitation of the 
electrolyte, not too great a conductivity of the latter, and a 
normal current-density, are the best auxiliaries for obtaining 
deposits of uniform thickness, and where these do not suffice 
recourse may be had for depressions to the hand anode (see 
later on). 

Current output. In the theoretical part it has already been 
stated that the separation-products of electrolysis are fre- 
quently subject to secondary decomposition. Thus, the hydro- 
gen escaping on the cathodes means a loss of electrolyzing 
effect of the current, and it is obvious that the quality of the 
deposit obtained does thereby not come up to the values which, 
according to the laws of Faraday, should be obtained. The 
quantities of deposit produced in practice referred to the theo- 
retically calculated quantities, are called the current-output. 

Reaction of the baths. A distinction is made between acid, 
alkaline, neutral, and potassium cyanide baths. The reaction 
of a bath is determined by means of suitable reagent papers. 
Thus, blue litmus paper, for instance, indicates the acid nature 
of a bath when by being dipped in it, it acquires a red color. 
All acids redden blue litmus paper, though many metallic 
salts of a perfectly neutral character produce the same change 
in color, and it is therefore necessary to make additional tests. 
Tropseolin paper, for instance, which possesses a yellow color, 
is only changed by mineral acids, the yellow color being con- 
verted into violet. A bath, which reddens blue litmus paper 
and colors tropseolin paper violet, contains without doubt, a 
free inorganic acid, while a bath which only reddens blue 
litmus paper, but does not change tropreolin paper does not 
contain a free inorganic acid, but an organic acid (citric* 
tartaric acids), and with a content of certain inorganic salts 
may also be free from organic acid. 



246 ELECTRO-DEPOSITION OF METALS. 

An alkaline reaction of the bath is indicated by red litmus 
paper acquiring a blue color, while neither blue or red litmus 
paper is changed when the electrolyte is neutral. 

In a normal state, potassium cyanide baths always show an 
alkaline reaction ; deviations from this condition will be later 
on referred to. 

The general qualifications which an electro-plating bath 
should possess are as follows : 

1. It should possess good conducting power. 

2. It must exert a sufficient dissolving effect upon the 
anodes. 

3. It must reduce the metal in abundance and in a reguline 
state. 

4. It must not be chemically decomposed by the metals to 
be plated, hence not by simple immersion ; the adherence of 
the deposit to the basis-metal being in this case impaired. 

5. It must not be essentially decomposed by air and light. 



CHAPTER VI. 

DEPOSITION OF NICKEL AND COBALT. 

1. Deposition of Nickel (Ni = 58.68 Parts by Weight). 

Although nickel-plating is of comparatively recent origin, 
it shall be first described, since chiefly by reason of the devel- 
opment of the dynamo-electrical machine it has steadily grown 
in popularity and become an industry of great magnitude and 
importance. The great popularity which nickel-plating enjoys 
is due to the excellent properties of the nickel itself — the 
almost silvery whiteness of the metal, its cheapness as com- 
pared with silver, and the hardness of the electro-deposited 
metal, which gives the coating great power to resist wear and 
abrasion ; its capability of taking a high polish ; the fact that 
it is not blackened by the action of sulphurous vapors which 
rapidly tarnish silver, and finally the fact; that it exhibits but 
little tendency to oxidize even in the presence of moisture. 

Properties of nickel. — Pure nickel is a lustrous, silvery-white 
metal with a slight steel-gray tinge. Its specific gravity varies 
from 8.3 (cast nickel plates) to 9.3 (wrought or rolled plates). 
It is slightly magnetic at the ordinary temperature, but loses 
this property when heated to 680° F. It melts at about the 
same temperature as iron, but is more fusible when combined 
with carbon. 

The metal is soluble in dilute nitric acid, concentrated nitric 
acid rendering it passive, i. e., insoluble. In hydrochloric and 
sulphuric acids it dissolves very slowly, especially when in a 
compact state. 

Certain articles, for instance, hot fats, strongly attack nickel, 
while vinegar, beer, mustard, tea and other infusions produce 
stains ; hence, the nickeling of culinary utensils or the use of 

(247) 



248 ELECTRO-DEPOSITION OP METALS. 

nickel-plated sheet iron for that purpose cannot be recom- 
mended. 

Nickel salts. The first requisite in preparing nickel baths is 
the use of absolutely pure chemicals, and in choosing the nickel 
salts to be especially careful that they are free from salts of iron, 
copper and other metals. Furthermore, it is not indifferent 
what kind of nickel salt is used, whether nickel chloride, nickel 
sulphate, the double sulphate of nickel and ammonium, etc., but 
the choice of the salt depends chiefly on the nature of the metal 
which is to be nickeled. There are a large number of general 
directions for nickel baths, of which nickel chloride, ammonio- 
nickel chloride, nickel nitrate, etc., form the active constituents, 
and yet it w T ould be a grave mistake to use these salts for nick- 
eling iron, because the liberated acid if not immediately and 
completely fixed by the anodes in dissolving, imparts to the iron 
objects a great tendency to the formation of rust. Iron objects 
nickeled in such a bath, to be sure, come out faultless, but in a 
short time, even if stored in a dry place, portions of the nickel 
layer will be observed to peel off, and by closely examining 
them it will be seen that under the deposit a layer of rust has 
formed which actually tears the nickel off. The use of nickel 
sulphates or of the salts with organic acids is, therefore consid- 
ered best. It might be objected that the liberated sulphuric 
acid produces in like manner a formation of rust upon the 
iron objects ; but according to long experience and many thor- 
ough examinations, such is not the case, the tendency to the 
formation of rust being only imparted by the use of the chlo- 
ride and nitrate. 

Of the nickel salts with organic acids, the citrate and tar- 
trate have been frequently employed. Nickel citrate in watery 
solution is not particularly well dissociated, requires a greater 
electro-motive force and is quite indifferent towards variations 
in the latter, this being the chief reason for its use in nickel- 
ing sharp ground instruments. Nickel lactate, according to 
Jordis's patent,* yields, to be sure, beautiful, lustrous deposits 

* Jordis, Elektrolyse wassriger Metallsalzlosungen, S. 78. 



DEPOSITION OF NICKEL AND COBALT. 249' 

in thin layers, but is not serviceable for heavy nickeling, 
since, as the inventor himself admits, deposits in thicker 
layers tear. Of materially greater advantage is the use of the 
combinations of nickel with the ethyl sulphates * and their 
derivatives. According to experiments made in Dr. Lang- 
bein's laboratory, the ethyl sulphate solutions of metals are 
very energetically dissociated and permit the production of 
very thick deposits without peeling off or tearing, such as 
cannot be obtained in the cold bath in any other nickel solu- 
tion ; they are distinguished by great homogeneity and 
toughness. 

Conducting salts. To decrease the resistance of the nickel 
solutions, conducting salts are added to them, which are also 
partially decomposed by the current. Like the use of nickel 
chloride in nickeling iron, an addition of ammonium chloride,, 
which is much liked, cannot be recommended, though the 
subsequent easy deposition of nickel with a comparatively 
weak current invites its employment. 

For copper and its alloys, zinc, etc., the chlorine combina- 
tions may be used, but for nickeling iron they must be avoided: 
as the source of future evils. 

The use of sodium acetate, barium oxalate, ammonium 
nitrate, ammonium-alum, etc., we consider unsuitable, and 
partially injurious, and are of the opinion that with few ex- 
ceptions, which will be referred to later on, potassium, 
sodium, ammonia or magnesia are best for bases of the con- 
ducting salts. 

The effect of the ions separated from the different conduct- 
ing salts varies very much ; the potassium ion acts different 
from the sodium ion, and the latter different from the mag- 
nesium ion, and an idea of this difference in action of the 
various ions can be formed by preparing, according to formula 
VIII, one nickel bath with potassium citrate and another with' 
sodium citrate. While the bath prepared with the potassium 

* German patent, No. 134, 736. 



"250 ELECTRO-DEPOSITION OF METALS. 

salt works quite well in the deeper portions on zinc, that pre- 
pared with the sodium salt is far less effective, and several 
other proofs derived from practice could be mentioned. An 
attempt to explain these facts must at present be abstained 
from as this suggestion cannot yet be proved by experiment so 
-that no objection to it could be raised. 

Other additions. — Some other additions to the nickeling bath 
which are claimed to effect a pure silver-white deposit have 
been recommended by various experts. Thus, the presence 
of small quantities of organic acid has been proposed ; for in- 
stance, boric acid by Weston, benzoic acid by Powell, and 
citric acid or acetic acid by others. The presence of small 
quantities of free acid effects without doubt the reduction of a 
whiter nickel than is the case with a neutral or alkaline solu- 
tion. Hence a slightly acid reaction of the nickeling bath, due 
to the presence of citric acid, etc., with the exclusion of the 
strong acids of the metalloids, can be highly recommended. 
The quantity of free acid, however, must not be too large, as 
this would cause the deposit to peel off. 

Boric acid recommended by Weston as an addition to nick- 
eling and all other baths, has a favorable effect upon the pure 
white reduction of the nickel, especially in nickeling rough 
castings, i. e., surfaces not ground. Weston claims that boric 
acid prevents the formation of basic nickel combinations on 
the objects, and that it makes the deposit of nickel more ad- 
herent, softer, and more flexible. Whether with a correct 
current-strength, basic nickel salts, to which the yellowish 
tone of the nickeling is said to be due, are separated on the 
•cathode, is not yet proved, and would seem more than doubt- 
ful. The action of the boric acid has not yet been scientific- 
ally explained, but numerous experiments have shown that 
4he deposition of nickel from nickel solution containing boric 
acid is neither more adherent nor softer and more flexible 
than that from a solution containing small quantities of a free 
organic acid. Just the reverse, the deposition is harder and 
more brittle in the presence of boric acid, and different results 



DEPOSITION OF NICKEL AND COBALT. 251 

may very likely be due to the employment of varying cur- 
rent-densities. 

In view of the fact that in the electrolysis of watery solutions, 
water also takes part in the processes enacted on the electrodes, 
and that the hydrogen appearing on the cathode promotes the 
formation of spongy, pulverulent and dull deposits, Marino * 
wants to substitute glycerin for water. Since many metallic 
salts dissolve only to a slight degree in glycerin, the content of 
metal in a glycerin bath is very low, and the resistance of the 
cold bath so great that enormous voltages are needed for the 
separation of metals, nickel, for instance, requiring more than 
"20 volts, and with an electro-motive force of 3 to 4 volts de- 
posits can only be produced when the baths have been heated 
to quite a high temperature. However, according to Foerster 
and Langbein's experiments, the deposits do not possess the 
good qualities claimed by the patent, and cannot be forced 
to such thickness as, for instance, is with the greatest ease 
attained in nickel ethyl-sulphate baths. 

The owners of the Marino patent have apparently them- 
selves recognized the disadvantages of the glycerin electrolyte, 
and have applied for a patent, according to which 15 to 50 per 
cent, of glycerin is to be added to solutions of metallic salts in 
water. The glycerin is claimed to act as depolarizer, and allow 
of the production of lustrous nickel deposits of great homo- 
geneousness. However, the correctness of these statements 
may be doubted, since by experiments made in this direction 
it was found impossible to produce a better technical effect 
with such an addition of glycerin than without it, in properly- 
prepared baths. 

It may here again be emphasized that the compositions of 
the electrolyte must vary according to the results desired, and 
that it is impossible to attain with one electrolyte all the pos- 
sible properties of the deposit. 

Moreover, the addition of glycerin to aqueous electrolytes 

* German patent, No. 104111. 



252 ELECTRO-DEPOSITION OF METALS. 

has for a long time been known through the English patents 
5300 and 22855, and it might be supposed that if such an 
addition were of special advantage it would have long ago 
come into general use. 

Effect of current-density. A slighter current-density always 
and under all conditions causes the deposition of a harder and 
more brittle nickel than a current of medium strength, while 
with too great a current-density, the metal is separated in pul- 
verulent form. However, as will be shown later on, nickel 
can also be deposited with a high current-density provided 
the baths are of proper composition, and agitated. 

Electro-motive force. The electro-motive force given for all 
the baths is valid for the normal temperature of 59° to 64.4° 
F. and an electrode-distance of 10 cm. It has previously 
been mentioned, that with an increasing temperature of the 
electrolyte its specific resistance becomes less, but grows as the 
temperature decreases, less electro-motive force being required 
in the first case, and more in the latter. 

The greater the electrode-distance in a bath is, the higher 
the electro-motive force which is required. A statement in 
figures of the changes in electro-motive force for the various 
electrode-distances will not be given because, on the one hand, 
the necessary electro-motive force is readily determined by a 
practical experiment, and, on the other, a calculation in ad- 
vance of the electro-motive force might lead to wrong con- 
clusions in so far as the specific resistance of the electrolyte is 
subject to change, and the value of the elect ro-motive force of 
the counter current varies very much for the objects sus- 
pended as cathodes, according to the nature of the basis-metal 
of which they are composed. For this reason a statement of 
the specific resistances of the bath prepared according to the 
directions given below is also omitted, because such state- 
ments would be valid only for freshly-prepared baths. 

Reaction of nickel baths. All nickel baths work best when 
they possess a neutral or slightly acid reaction. Hence blue 
litmus-paper should be only slightly reddened, and red congo- 



DEPOSITION OF NICKEL AND COBALT. 253 

paper must not be changed at all. Baths prepared with 
boric acid form an exception, as they may show quite a strong 
acid reaction. An alkaline reaction of nickel baths is abso- 
lutely detrimental, such baths depositing the metal dull and 
with a yellowish color, and do not yield thick deposits. 

Formulas for nickel baths. I. The most simple nickel bath 
consists of a solution of 8 parts by weight of pure nickel am- 
monium sulphate in 100 parts by weight of distilled water. 

Electro-motive force at 10 cm. electrode-distance, 3.0 volts. 

CurrenUdensity, 0.3 ampere. 

The solution is prepared by boiling the salt with the cor- 
responding quantity of water, using in summer 10 parts of 
nickel salt to 100 of water, but in winter only 8 parts, to pre- 
vent the nickel salt from crystallizing out. This bath, which 
is frequently used, possesses, however, a considerable degree 
•of resistance to conduction, and hence requires a strong cur- 
rent for the deposition of the nickel. It also requires cast- 
nickel anodes, since with the use of rolled anodes nickeling 
proceeds in a very sluggish manner. However, the cast 
anodes rapidly render the bath alkaline, necessitating a fre- 
quent correction of the reaction. The alkalinity is overcome 
by carefully adding dilute sulphuric or citric acid to neutral 
•or slightly acid reaction. 

To decrease the resistance, recourse has been had to certain 
conducting salts, and, below, the more common nickel baths 
will be discussed, together with their mode of preparation and 
action, as well as their availability for certain purposes. 

II. Nickel ammonium sulphate 17 ozs., ammonium sul- 
phate 17 ozs., distilled water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 1.8 to 2 

TOlts. 

Current-density, 0.35 ampere. 

Boil the salts with the water, and, if the solution is too acid, 
restore its neutrality by ammonia; then gradually add solution 
•of citric acid until blue litmus-paper is slowly but perceptibly 
reddened. The bath deposits rapidly, it possessing but little 



254 ELECTRO-DEPOSITION OF METALS. 

resistance, and all metals (zinc, lead, tin and Britannia, after 
previous coppering) can be nickeled in it. However, upon 
rough castings and iron, a pure white deposit is difficult to- 
obtain, frequent scratch-brushing with a medium hard-steel 
brush being required. On account of the great content of 
sulphate of ammonium in the bath, the nickel deposit piles up 
especially on the lower portions of the objects, which, in con- 
sequence, readity become dull (burn or over-nickel, for which 
see later on), while the upper portions are not sufficiently 
nickeled. For this reason the objects must be frequently 
turned in the bath so that the lower portions come uppermost. 
This piling-up of the deposit also frequently prevents the- 
latter from acquiring a uniform thickness. 

III. Nickel ammonium sulphate 25J ozs., ammonium sul- 
phate 8 ozs., crystallized citric acid If ozs., water 10 to 12 
quarts. 

Electro-motive force at 10 cm. electrode-distance, 2.0 to 2.2 
volts. 

Current-density, 0.34 ampere. 

The bath is prepared in the same manner as the preceding, 
the salts being dissolved in boiling water, and ammonia added 
until blue litmus paper is only slightly reddened. , 

This bath was formerly in general use in this county and 
is to some extent at present employed, especially for nickeling 
ground articles. It has the drawback of requiring very care- 
ful regulation of the current to avoid peeling off. According 
to experiments made by Dr. Langbein, it would be better to 
decrease the content of ammonium sulphate to 0.8 oz. 

The reaction of this bath should be kept only very slightly 
acid or, still better, neutral, and it is best to use an equal 
number of cast and rolled nickel anodes. 

If, after working for some time, the objects nickel dark, an 
addition of nickel sulphate is advisable, if the reaction is cor- 
rect and possibly not alkaline. 

IV. Nickel-ammonium sulphate 23 ozs., ammonium chlo- 
ride (crystallized) 11| ozs., water 10 to 12 quarts. 



DEPOSITION OF NICKEL AND COBALT. 255' 

Electro-motive force at 10 cm. electrode-distance, 1.5 volts. 

Current-density, 0.55 ampere. 

The bath is prepared in the same manner as given for II 
and III. It requires exclusively rolled anodes, nickels very 
rapidly and quite white, but the deposit is soft and care must 
therefore be had in polishing upon cloth or felt bobs, the 
corners and edges of the objects particularly requiring careful 
handling. On account of the danger of peeling off a heavy 
deposit of nickel cannot be obtained in this bath, since, in 
consequence of the rapid deposition the layer of nickel con- 
denses and absorbs hydrogen, is formed with a coarser 
structure and turns out less uniform and dense. These phe- 
nomena are a hindrance to a heavy deposit which, if it is to 
adhere, must be homogeneous and dense. 

As previously mentioned, baths with the addition of chlorides,, 
as well as those prepared with nickel chloride and nickel nitrate, 
are not suitable for the solid nickeling of iron. They are, how- 
ever, well adapted to the rapid light nickeling of cheap brass 
articles on which no great demands for solidity and durability 
are made. To obtain nickeling of a whiter color, only 7 ozs. 
in place of 11 J ozs. of ammonium chloride and 3 J ozs. of 
boric acid may be dissolved with the assistance of heat. The 
bath then requires 1.8 to 2 volts. 

V. Nickel chloride (crystallized) 17 J ozs., ammonium 
chloride (crystallized) 17J ozs., water 12 to 15 quarts. 

Electro-motive force at 10 cm. electrode-distance, 1.75 to 2: 
volts ; for zinc, 2.8 to 3 volts. 

Current-density, 0.5 ampere. 

This bath is prepared by dissolving the salts in luke-warm 
water and adding ammonia until the bath shows a very 
slightly acid, or a neutral, reaction. The bath deposits 
readily and is especially liked for nickeling zinc castings. 

All the drawbacks of the preceding bath as regards the 
nickeling of iron apply also to this bath, onky to a still greater 
extent. Rolled nickel anodes have to be exclusively used. 



256 ELECTRO-DEPOSITION OF METALS. 

Nickel Baths Containing Boric Acid. 

VI. Weston recommends the following composition for 
nickel baths: Nickel chloride 17J ozs., boric acid 7 ozs., 
water 20 quarts ; or nickel-ammonium sulphate 35 ozs., boric 
acid 17 \ ozs., water 25 to 30 quarts. Both solutions are said 
to be improved by adding caustic potash or caustic soda so 
long as the precipitate formed by the addition dissolves. 

These compositions, however, cannot be recommended, be- 
cause the baths work faultlessly for a comparatively short time 
only. All kinds of disturbing phenomena very soon made 
their appearance, the deposit being no longer white but black- 
ish, and the baths soon failing entirely. Kaselowsky's for- 
mula yields similar results. This bath is prepared by dissolv- 
ing, with the assistance of heat, 35£ ozs. of nickel-ammonium 
sulphate and 17| ozs. of boric acid in 20 quarts of water. 
This bath also generally fails after two or three months' use. 
The cause of this has to be primarily sought for in the fact 
that baths prepared with boric acid require, according to their 
composition, a definite proportion between rolled and cast 
nickel anodes. If rolled anodes are exclusively used, free 
sulphuric acid is soon formed, which causes energetic evolu- 
tion of hydrogen on the articles, but prevents a vigorous 
deposit and imparts to the latter a tendency to peel off. The 
same thing happens when a nickel salt not entirely neutral 
has been used in the preparation of the bath. If, on the 
Other hand, cast nickel anodes alone are employed, the bath 
soon becomes alkaline, with turbidity and the formation of 
slime, and the deposit turns out gray and dull before it pos- 
sesses sufficient thickness. 

From the foregoing it will be readily understood that the 
nickel salt used must be neutral, and that the proportion of 
rolled to cast anodes must be so chosen that the free sulphuric 
acid formed on the cast anodes is neutralized, but that the 
acidity of the bath dependent on the free boric acid is con- 
stantly maintained. 



DEPOSITION OP NICKEL AND COBALT. 257 

A recent author argues in support of Haber's proposition 
>that the effect produced by the use of mixed anodes, i. e., 
rolled and cast anodes, might be attained by regulating the 
anode current-density by the use of definite dimensions of the 
anodes in such a way that the electrolyte, as regards its com- 
position, remains constant. For practical purposes this would 
•only be feasible without trouble, if approximately the same 
object-surface is always present in the bath, otherwise the 
maintenance of the adequate anode current-density must be 
managed by taking out or suspending anodes according to 
the varying object-surfaces. However, this is far more trouble- 
some, and the use of mixed anodes is decidedly to be pre- 
ferred, it having been shown in the Galvanic Institute of Dr. 
George Langbein, that by this means the reaction of a bath 
•can for years be kept constant even with considerable varia- 
tions in the size of the object-surface. 

Such a bath containing boric acid may advantageously be 
prepared as follows : 

VII. Nickel-ammonium sulphate 21 ozs., chemically pure 
nickel carbonate If ozs., chemically pure boric acid (crys- 
tallized) 10| ozs., water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 2.25 to 2.5 
volts. 

Current- density, 0.35 ampere. 

Boil the nickel-ammonium sulphate and the nickel carbon- 
ate * in the water until the evolution of bubbles of carbonic 
acid ceases and blue litmus-paper is no longer reddened. 
After allowing sufficient time for settling, decant the solution 
from any undissolved nickel carbonate, and add the boric 
acid. Boil the whole a few minutes longer, and allow to cool. 
If the nickel salt contains no free acid, boiling with the nickel 
carbonate may be omitted. The solution shows a strongly acid 
reaction, which must not be removed by alkaline additions. 

The proportion of cast to rolled anodes used in this bath is 

* In place of nickel carbonate, nickel hydrate may as well be used. 

17 



258 ELECTRO-DEPOSITION OF METALS. 

dependent on the quality of the anodes. The use of readily- 
soluble cast anodes requires the suspension in the bath of more 
rolled anodes than when cast anodes dissolving with difficulty 
are employed, since the surfaces of the latter, in consequence 
of rapid cooling, are not readily attacked. The proportion has 
likewise to be changed, with the use of soft- or hard-rolled 
anodes. Hence the proper proportion will have to be estab- 
lished by frequently testing the reaction of the bath. For this 
purpose the following rules may be laid down : Blue litmus- 
paper must always be perceptibly and intensely reddened, but 
congo-paper should not change its red color, for if the latter 
turns blue it is an indication of the presence of free sulphuric 
acid in the bath, which has to be neutralized by the careful 
addition of solution of soda or potash until a fresh piece of 
congo-paper dipped in the bath remains red. Ammonia can- 
not be recommended for neutralizing free sulphuric acid in 
this bath. Red litmus paper must retain its color, for if it 
turns blue, the bath has become alkaline, and fresh boric acid 
has to be dissolved in the previously heated bath until a fresh 
piece of blue litmus paper acquires an intense red color, or 
pure dilute sulphuric acid has to be added to the bath, stirring 
constantly, until blue litmus paper is reddened, avoiding, how- 
ever, an excess which is indicated b} r red congo paper turning 
blue. 

This bath is equally well adapted for nickeling ground ob- 
jects, as well as for rough castings, the latter acquiring a pure 
white coating of nickel if thoroughly scratch-brushed, and the 
bath shows a normal acid reaction. 

Below are given a few other formulae for nickel baths which 
may be advantageously used for special purposes, but not for 
nickeling all kinds of metals with equally good results. 

VIII. Nickel sulphate 10 J ozs., potassium citrate 7 ozs., 
ammonium chloride 7 ozs., water 10 to 12 quarts. 

For copper and copper-alloys : Electro-motive force at 10 cm. 
electrode-distance, 1.5 to 1.7 volts. 

Current-density, 0.45 to 0.5 ampere. 



DEPOSITION OF NICKEL AND COBALT. 259 

For zinc : Electro-motive force at 10 cm. electrode-distance, 
2 to 2.5 volts. 

Current density, 0.8 to 1 ampere. 

To prepare the bath dissolve 10J ounces of nickel sulphate 
and 3J ounces of pure crystallized citric acid in the water ; 
neutralize accurately with caustic potash, and then add the 
ammonium chloride. This bath is especially adapted for the 
rapid nickeling of polished, slightly coppered zinc articles, 
for instance, tops, candlesticks, mountings, etc. Deposition is 
effected with a very feeble current, without the formation of 
black streaks, such as are otherwise apt to appear in nickeling 
with a weak current. The deposit itself is dull and somewhat 
gray, but acquires a very fine polish and pure white color by 
slight manipulation upon the polishing wheels. With a 
stronger current the bath is also suitable for the direct nickel- 
ing of zinc articles; it must, however, be kept strictly neutral. 
The bath works with rolled anodes, and when it has become 
alkaline, requires a correction of the reaction by citric acid. 

IX. Nickel phosphate, 6J ozs., sodium pyrophosphate, 26J 
ozs., water, 10 quarts. 

For copper and its alloys : Electro-motive force, at 10 cm. 
electrode-distance, 3.5 volts. 

Current density, 0.5 ampere. 

For the preparation of the nickel phosphate dissolve 12 ozs. 
of nickel sulphate in 3 quarts of warm water and 10 ozs. of 
sodium phosphate in another 3 quarts of ^warm water. Mix 
the two solutions, stirring constantly, and filter off the pre- 
cipitated nickel phosphate. 

Dissolve the sodium pyrophosphate in 8 quarts of warm 
water, add the nickel phosphate, which soon dissolves by thor- 
ough stirring, and make up the bath to 10 quarts by adding 
w r ater. 

This bath yields a dark nickeling particularly upon sheet 
zinc and zinc castings, and may be advantageously used for 
decorative purposes where darker tones of nickel are required. 
-For zinc, work with 3.8 volts and 0.55 ampere. 



260 ELECTRO-DEPOSITION OF METALS. 

For the same purpose a nickel solution compounded^ with a 
large quantity of ammonia, hence an ammoniacal nickel 
solution has been recommended. However, experiments with 
this solution alwaj^s yielded lighter tones than bath IX. 
Special advantages cannot be claimed for this so-called dark 
nickeling since in arsenic and antimony we have more effective 
and more reliable expedients. 

Black nickeling. Black deposits of nickel are frequently 
used particularly for decorative purposes. For the production 
of such deposits general directions may be given as follows: 
1. A strong bath has to be used. 2. Apply a weak current. 
For the production of a uniform black deposit the current- 
strength should not exceed 1 volt. From the manner in 
which the deposit commences to form, it can readily be recog- 
nized whether the current is of suitable strength. The first 
film of deposit upon the object is iridescent, i. e., shows rain- 
bow colors and does not extend over the entire surface. The 
deposit next acquires a bluish tone until finally a black coat- 
ing is formed. If the deposit acquires immediately in the 
commencement of the operation a uniform color, the current 
is too strong. The deposit should form slowly ; it should, as 
mentioned above, at first be iridescent and the black deposit 
appear only after one or two minutes. It is of sufficient 
thickness as soon as the desired color appears. Very thick 
deposits are apt to peel off, they being more or less brittle. 
With the use of a weak current 30 to 60 minutes will be re- 
quired for the production of a deposit of sufficient thickness. 
4. A large number of nickel anodes should be used. Old 
anodes are to be preferred, they yielding nickel more readily 
than new ones. 5. Any acid which may be present in the 
bath should be neutralized by the addition of nickel carbon- 
ate, a neutral bath yielding a better deposit than one even 
only slightly acid. 

A black nickel bath of the following composition yields a 
very uniform black deposit : Water 4J quarts, double sul- 
phate of nickel and ammonium 10 ozs., ammonium sulpho- 



DEPOSITION OF NICKEL AND COBALT. 261 

cyanate 1 oz., zinc sulphate 1 oz. This bath practically con- 
tains exclusively double nickel salts which dissolve in water. 
If in cold weather crystallizing takes place, the bath has to 
be heated. It is best to keep the temperature of the bath at 
from 70° to 100° F.; at a higher temperature the deposit 
readily acquires a gray color. At a temperature of below 
59° F. some nickel salts readihy crystallize out, and besides 
the bath does not work well. 

A gray color of the deposit is an indication of too strong a 
current, this being also the case when streaks are formed upon 
the object. With the use of an old bath it may happen that 
it becomes acid and it will be noticed that a black coating is 
not produced, even by reducing the current-strength. The 
bath then very likely contains free acid, and the best means 
of neutralizing it is the addition of nickel carbonate. In case 
the latter is not available, ammonia may be used. Test the 
bath with litmus paper. If before adding the nickel carbon- 
ate or ammonia, blue limus paper when dipped into the bath 
turns red, the bath is acid. Add nickel carbonate until no 
more of it dissolves, although a small excess is no disadvan- 
tage. On the other hand, with the use of ammonia care must 
be had that no more than required for neutralization is added. 
When the limit is reached at which the color of either blue 
or red litmus paper is no longer changed, no more ammonia 
should be added. 

Black nickel deposits frequently come from the bath with 
the proper black color and otherwise without defect, but when 
rinsed and dried have a brown tone. This can be removed 
by immersion in chloride of iron solution. The latter does 
not attack the black nickel deposit, provided the objects are 
not left too long in it, a moment's immersion being sufficient, 
after which they are rinsed and dried. The chloride of iron 
bath is composed of: Chloride of iron 8J ozs., hydrochloric 
acid 18 drachms, water 4j quarts. 

Black nickel deposits when exposed to the influence of 
atmospheric air gradually acquire a brown color which, how- 



262 ELECTRO-DEPOSITION OF METALS. 

ever, is only superficial and can be wiped off. To prevent 
such tarnishing a coat of lacquer is as a rule applied to the 
nickeled object. 

Black nickel deposits are much used as a priming in the 
application of mat black lacquers to automobile parts and 
for other purposes, where as durable a coating as possible is 
desired. If the lacquer is applied without previously giving 
the brass a suitable black nickel deposit, every tiny scratch or 
peeling-off becomes perceptible, which is prevented by the 
black nickel deposit underneath the lacquer. 

A black nickel bath of the following composition has been 
recommended by Blauet : Water 95 gallons, nickel-ammonium 
sulphate 12 ozs., potassium sulphocyanide 2£ ozs., copper 
carbonate 2 ozs., arsenious acid 2 ozs. 

Dissolve the nickel salt in the water and add the potassium 
sulphocyanide. Then dissolve, at about 176° F., the copper 
carbonate by treatment with ammonium carbonate or potas- 
sium cyanide, and add the solution, while lukewarm, to the 
bath. Finally add the arsenious acid. If in time a gray 
sediment is formed, some potassium sulphocyanide and copper 
carbonate have to be added. 

X. A fairly good nickel bath for many purposes is obtained 
from a solution of nickel-ammonium sulphate 22J ozs., mag- 
nesium sulphate 11J ozs., water 10 to 12 quarts. 

For iron and copper alloys : Electro-motive force at 10 cm. 
electrode-distance, 4 volts. 

Current-density, 0.2 ampere. 

This bath deposits with ease, and a heavy coating can be 
produced on iron without fear of the disagreeable conse- 
quences of bath IV. Even zinc may be directly nickeled in 
it with a comparatively feeble current. The deposit, how- 
ever, turns out rather soft, with a yellowish tinge, and the 
bath does not remain constant, but -fails after working at the 
utmost three or four months, even cast anodes being but little 
attacked. 

For the production of very thick deposits a bath composed 



DEPOSITION OF NICKEL AND COBALT. 263 

of nickel sulphate 17.63 ozs. and sodium citrate 17.63 ozs. 
dissolved in 2f gallons of water has also been recommended. 
Pfanhauser has changed these proportions to nickel sulphate 
14.11 ozs. and 12.34 ozs. sodium citrate dissolved in 2f gal- 
lons of water. This bath is said ' to be available chiefly for 
the production of nickel cliches and thick deposits. It has, 
however, the drawback of all nickel baths prepared with large 
quantities of organic combinations of requiring a high electro- 
motive force and of readily becoming mouldy. It can, how- 
ever be highly recommended for nickeling articles with sharp 
edges and points, for instance, knives, scissors, etc., it being 
quite indifferent towards changes in the current proportions, 
so that even with • a higher than the normal electro-motive 
force and a greater current-density the objects do not readily 
over-nickel. The deposit is very soft, and hence in grinding 
such nickeled instruments peeling-olf of the deposit takes 
place more rarely than with objects nickeled in baths of dif- 
ferent composition. Electro-motive force at 10 cm. electrode- 
distance, 3 volts ; current-density, 0.35 ampere. 

According to an English formula, 17.63 ozs. nickel sulphate, 
9 ozs. 5 J drachms tartaric acid and 2.4 ozs. caustic potash are 
dissolved in 2f gallons of water. The results with this bath 
were only moderate. 

It has not been deemed necessary to give additional form- 
ulas for nickel baths, because no better results were obtained 
from other receipts which have been published and which 
have been thoroughly tested, than from those given above. 
In most cases success with them fell far short of expectation. 

Some authors have recommended for nickeling a solution 
of nickel cyanide in potassium cyanide, but experiments 
failed to obtain a proper deposition of nickel. 

The addition of carbon disulphide to nickel baths, which 
has been recommended by Bruce, is not advisable. Accord- 
ing to Bruce, such an. addition prevents the nickel deposit 
from becoming dull when reaching a certain thickness, but 
repeated experiments made strictly in accordance with the 
directions given did not confirm this statement. 



264 ELECTRO-DEPOSITION OF METALS. 

The general remark may here be adder] that freshly pre- 
pared nickel baths mostly work correctty from the start, 
though it may sometimes happen that the articles first nickeled 
come from the bath with a somewhat darker tone. In this 
case suspend a few strips of iron or brass-sheet to the object- 
rod; allow the bath to work for one or two hours, when 
nickeling will proceed faultlessly. If, however, such should 
not be the case, ascertain by a test with the hydrometer 
whether the specific gravity of the bath is too high. If the 
deposit does not turn out light, even after dilution, it is very 
likely that the nickel salt contains more than traces of copper, 
or, with black-streaked nickeling, zinc. 

It has also been observed that the deposit frequently peels 
off when, for the purpose of neutralization, additions have 
been made to the nickel baths. This phenomenon disappears 
in a few days, but it demonstrates that, instead of correcting 
the reaction of the bath by the addition of acids or alkalies, it 
should be done by increasing the rolled anodes in case the 
bath shows a tendency to become alkaline, or to increase the 
cast anodes in case the bath becomes too acid. 

A few words may here be said in regard to what may be 
termed & nickel bath without nickel salt. t It simply consists of 
a 15 to 20 per cent, solution of ammonium chloride, which 
transfers the nickel from the anodes to the articles. Cast 
anodes are almost exclusively used for the purpose, and depo- 
sition may be effected with quite a feeble current. Before 
the solution acquires the capacity of depositing, quite a strong 
current has to be conducted through the bath until the com- 
mencement of a proper reduction of nickel. This bath is 
only suitable for coloring very cheap articles, it being impos- 
sible to produce solid nickeling with it. It is here mentioned 
because it may serve as a representative of a series of other 
electro-plating baths in which the transfer of the metal is 
effected by ammonium chloride solution without the use of 
metallic salts, for instance, iron, zinc, cobalt, etc. 

Prepared nickel salts. As previously mentioned, there is a 



DEPOSITION OF NICKEL AND COBALT. 265 

large number of receipts for nickel baths, some of them being 
entirely unsuitable, while others are only available for certain 
purposes. Hence, it is impossible, even for the skilled oper- 
ator, to separate the good receipts from the bad ones, if he is 
not qualified to do so by many years' experience and a thor- 
ough knowledge of chemistry. The choice is still more diffi- 
cult for the beginner and layman, and it is recommended to 
them to get their supply of suitable baths from well-known 
dealers in electro-plating supplies. 

By prepared nickel salts are understood preparations which, 
in addition to the most suitable nickel salt, contain the re- 
quired conducting salt for the decrease of the resistance, and 
further such additions as promote a pure white separation of 
nickel, and are necessary for the continuously good working 
of the bath. 

Correction of the reaction of nickel baths. When after long 
use a nickel bath has become alkaline, which is readily deter- 
mined by a test with litmus paper, this defect can in a few 
minutes be overcome by the addition of an acid, and accord- 
ing to the composition of the bath, its neutrality or slightly 
acid reaction can be restored by citric, acetic, sulphuric, boric 
acids, etc. The use of hydrochloric acid for this purpose, 
which has been recommended, is not advisable. In most 
cases it will be best to employ dilute sulphuric acid, provided 
an excess of it be avoided, which is recognized by red congo- 
paper turning blue. 

When a bath contains too much free acid, the latter may be 
removed by an addition of ammonia, ammonium carbonate, 
potash or nickel carbonate, the choice of the agent to be used 
depending on the composition of the bath. 

Thick deposits in hot nickel baths. Nickel baths, more or less 
highly heated, have for years been used for nickeling, the 
purpose being, on the one hand, the production in a shorter 
time of a thick deposit, and on the other, it was expected that 
the product thus obtained would become especially dense in 
consequence of the contraction in cooling. 



266 ELECTRO-DEPOSITION OF METALS. 

The results obtained in heated baths were, however, un- 
satisfactory, since, if the current was not carefully regulated, 
the deposit peeled off readily, and the polished nickeling 
became dull on exposure to the air. 

The unsatisfactory results might primarily have been due 
to an unsuitable composition of the electrolytes. Foersters's * 
experiments have shown that almost perfectly smooth de- 
posits of 0.5 to 1 millimeter thickness may be obtained in 
absolutely neutral nickel solutions with a high content of 
nickel — 1 oz. or more per quart — if kept at a temperature of 
122° to 194° F., for instance, in solutions containing 5 ozs. 
nickel sulphate per quart, at 167° to 176° F. Electro-motive 
force, at an electrode-distance of 4 cm., 1.3 volts; current- 
density, 2 to 2.5 amperes. 

Exhaustive experiments made by Dr. George Langbein led 
to the result that deposits of great thickness may also be pro- 
duced in slightly acidulated nickel baths of suitable composi- 
tion, at a temperature kept constant at from 185° to 194° F. 
In a bath which contained 12.34 ozs. of nickel sulphate and 
6.34 ozs. of sodium sulphate or magnesium sulphate per 
quart, and which was slightly acidulated with acetic acid, 
deposits of 0.5 millimeter thickness were in 12 hours obtained, 
the current-density amounting to 4 amperes. 

For nickeling flat objects the current-density may, however, 
be materially increased, one of up to 8 amperes or more being 
permissible. By reason of the rapidity with which thick de- 
posits can be produced in hot baths of the above-mentioned 
composition, the term quick nickeling has been applied to this 
process. 

Independent of Dr. Langbein, Dr. Kugel discovered that 
thick deposits of nickel can be obtained in a hot nickel bath 
of nickel sulphate and magnesium sulphate very slightly 
acidulated with sulphuric acid.f 

* Zeitschrift fur Elektrochemie, 1897 to 1898, p. 160. 
f German patent, 117054. 



DEPOSITION OF NICKEL AND COBALT. 267 

While, in order to avoid the formation of roughness and 
bud-like excrescences, Foerster found agitation of the electro- 
lytes of the composition mentioned by him of advantage, Dr. 
Langbein obtained smoother deposits when the electrolyte was 
not mechanically agitated, and the fluid was only slowly mixed 
through by heating with a steam coil. 

Upon flat objects, for instance, sheets, very uniform deposits 
1 millimeter or more in thickness are very rapidly obtained, as 
well as upon round objects, if care be taken to have, by the 
use of anodes of the same shape, a uniform anode-distance 
from all object surfaces. However, the production of such 
deposits of entirely uniform thickness upon articles with high 
relief has thus far not been successfully accomplished by Dr. 
Langbein with the use of the above-mentioned electrolytes. 

Thick deposits in cold nickel baths. By the use of an electro- 
lyte which contains nickel ethyl sulphate (German patent, 
No. 134736) or the ethyl sulphates of the alkalies or alkaline 
earths, deposits of any desired thickness can be produced if 
the bath be constantly agitated by mechanical means or the 
introduction of hydrogen. Agitation by blowing in air is not 
permissible on account of oxidation of the ethyl-sulphate 
combinations by the oxygen of the air. 

Continued experiments with such ethyl-sulphate combina- 
tions by Dr. G. Langbein & Co. resulted in finding formulas 
for prepared nickel salts from the solutions of which thick de- 
posits of nickel capable of being polished can in a few minutes 
be obtained in the cold way. The formulas for these different 
prepared nickel salts will not be given, as they are protected 
by patents. The salts -are known in commerce as Mars, 
Lipsia, Germania and Neptune. 

In an electrolyte of given composition, which has to be 
constantly kept slightly acid with acetic acid, nickeling may 
for weeks be carried on at the ordinary temperature without 
any peeling-off of the deposit being noticed, and, in this 
respect, this bath surpasses all other known baths. In the 
course of six weeks, Dr. Langbein has produced upon gutta- 



268 ELECTRO-DEPOSITION OF METALS. 

percha matrices, galvanoplastic nickel deposits 6 millimeters- 
in thickness, the metal proving thoroughly homogeneous and 
firmly united throughout its entire thickness. 

Coehn and Siemens * found that from electrolytes which 
contain nickel salts and magnesium salts, weighable quantities 
of magnesium are under certain conditions separated together 
with the nickel, and they succeeded in depositing alloys con- 
taining approximately 90 per cent, of nickel and 10 per cent, 
of magnesium. According to the above-mentioned authors, 
the behavior of the nickel-magnesium alloys in the electrolytic 
separation differs essentially from that of nickel, they showing 
especially no tendency towards peeling off. 

Nickel anodes. Either cast or rolled nickel plates are used 
as anodes, they, of course, having to be made of the purest 
quality of nickel. Every impurity of the anode passes into the 
bath, and jeopardizes, if not at first, then finally, its successful 
working. Rolled anodes dissolve with difficulty and cast 
anodes, as a rule, with ease. If the latter dissolve only with 
difficulty they fail in their object of replacing the nickel metal 
withdrawn from the bath by the nickeling process. 

As regards solubility, electrolytically produced nickel anodes 
stand between rolled and cast anodes. 

The anodes should not be too thin, otherwise they increase 
the resistance. For small baths rolled anodes 2 to 3 milli- 
meters thick are generally used. For larger baths, it is better 
to use plates 3 to 10 millimeters thick, while the thickness of 
cast anodes may vary from 3 to 10 millimeters, according to 
their size. 

Attention may here be called to the elliptic anodes, Fig. 
110, patented by the Hanson & Van Winkle Co., Newark, 
N. J. The great advantage claimed in the use of these 
elliptic anodes over the old style flat plate is the uniformity 
of deposit as disintegration takes place from all sides of the- 
anode ; consequently the molecules are distributed uniformly 

*Zeitschrift fur Elektrochemie, 1902, S. 591. 



DEPOSITION OF NICKEL AND COBALT. 



269 



Fig. 110. 





throughout the solution, and not only hasten the deposit, but 
.give a heavier deposit in a given time. Another important 
feature in these anodes is 
the fact that they wear 
down evenly to a small, 
narrow strip, and when 
worn down to such a 
point that it seems de- 
sirable to put in more 
nickel, the old ones which 
take up practically no 
room in the tank, can re- 
main until entirely con- 
sumed, and as a result 
there is practically no 
scrap nickel to dispose of 
at half price. Fig. Ill 
shows the small loss in 
the use of the elliptic 
anode. The weight of 
the orginal plate was 16 
pounds. Percentage of 
waste only 5 per cent. 

Fig. 112 shows the or- 
iginal shape of the flat 
plate still largely used 
.and the character of the 
wear. The top part of 
the scrap-plate with its 
two ears is almost as 
heavy as the same section 
•of the original plate. The 
■original weight of the 
plate was 13| lbs. Waste 

2 lbs. Percentage of waste 14.6 per cent. Another form of 
the old-style plate is shown in Fig. 113. The original weight 



270 



ELECTRO-DEPOSITION OP METALS. 



was 17 J lbs. Weight of scrap 4| lbs. Perceiitage of waste 
27.4 per cent. The examples shown in the illustrations were 



Fig. 111. 



TTTTt 
- | - 



10 oz. 



12 oz. 



14 oz. 



? 



13 oz. I0 °z 



16 LBS, 



taken from a lot of scrap returned to the manufacturers. The 
scrap from the elliptic anode came from a large stove concern 



Fig. 112. 



Fig. 113. 





--'--- -— " 4 1 lbs. 

and the flat scrap also from a stove manufacturer. Elliptic 
anodes are furnished in all commercial metals. 



DEPOSITION OF NICKEL AND COBALT. 271 

The use of insoluble anodes of retort carbon or platinum, 
either by themselves or in conjunction with nickel anodes, as 
frequently recommended by theorists, is not advisable. The 
harder and the less porous the nickel anode is, the less it is 
attacked in the bath and the less it fulfills the object of keeping 
constant the metallic content of the solution. On the other 
hand, the softer and the more porous the anode is, the more 
readily it dissolves, because it conducts the current better and 
presents more points of attack to the bath ; and the more it is 
dissolved, the more metal is conveyed to the bath. With the 
sole use of rolled anodes and working with a feeble current, 
free acid is formed in the bath; on the other hand, by working 
with cast anodes alone, the bath readily becomes alkaline. 
Now it would appear that the possibility of a bath also becom- 
ing alkaline even with the sole use of rolled anodes, especially 
when working with a strong current, has led to the proposition 
of suspending in the bath, besides the nickel anodes, a suffi- 
cient number of insoluble anodes in order to effect a constant 
neutrality of the bath. It would lead too far to go into the 
theory of the secondary decompositions which take place in a 
nickel bath to prove that, though neutrality is obtained, it can 
only be done at the expense of the metallic content of the 
bath. Hence this impracticable proposition will here be over- 
thrown by practical reasons, it only requiring to be demon- 
strated that in baths becoming alkaline the content of nickel 
also decreases steadily though slowly. This fact in itself shows 
that in order to save the occasional slight labor of neutralizing 
the bath, the decrease of the metallic content should not be 
accelerated by the use of insoluble anodes. 

For larger baths the use of expensive platinum anodes as 
insoluble anodes need not be taken into consideration, be- 
cause for large surfaces of objects correspondingly large sur- 
faces of platinum anodes would have to be present, as other- 
wise the resistance of thin platinum sheets would be consider- 
able. But such an expensive arrangement would be justifiable 
only if actual advantages were obtained, which is not the- 



272 ELECTRO-DEPOSITION OF METALS. 

case, because, though the platiiium does absolutely not dis- 
solve, the deficiency of metallic nickel in the bath caused by 
such anodes must in some manner be replaced. 

The insoluble anodes of gas-carbon, which have frequently 
been proposed, are attacked by the bath. Particles of carbon 
become constantly detached, and floating upon the bath, de- 
posit themselves upon the objects and cause the layer of 
nickel to peel off. Furthermore, by the use of nickel anodes 
in conjunction with carbon anodes, the current, on account of 
the greater resistance of the latter, is forced to preferably take 
its course through the metallic anodes, in consequence of 
which the articles opposite the nickel anodes are more thickly 
nickeled than those under the influence of the carbon anodes. 
With larger objects this inequality in the thickness of the de- 
posit is again a hindrance to obtaining layers of good and 
uniform thickness, such as are required for solid nickeling. 
Since the current preferably seeks its compensation through 
these separate metallic anodes, they are more vigorously 
attacked than when nickel plates only are suspended in the 
bath. 

With nickel baths which contain a considerable amount of 
ammonium chloride, the use of a few carbon anodes along with 
the rolled nickel anodes may be permissible, since these baths 
strongly attack even the rolled anodes, and thereby convey to 
the bath sufficient quantities of fresh nickel. Such baths con- 
taining ammonium chloride, as a rule, become very rapidly 
alkaline, so that frequent neutralization becomes inconvenient. 
However, in this case, it is advisable to place the carbon 
anodes in small linen bags which retain any particles of car- 
bon becoming detached, the latter being thus prevented from 
depositing upon the, articles in the bath. 

According to long practical experience, the best plan is to 
use rolled and cast anodes together in a bath which does not 
contain chlorides, and to apportion the anode surface so that 
an anode-rod, about f of its length, is fitted with anodes. If, 
for instance, a tank is 120 centimeters long in the clear and 50 



DEPOSITION OF NICKEL AND COBALT. 273 

centimeters deep, the width of the nickel anodes laid alongside 
one another should be about 80 centimeters, and their length 
about | of the depth of the tank, hence 30 centimeters. For 
each anode-rod, 8 anodes, each 30 centimeters long and 10 
centimeters wide, would, therefore, be required. 

The proportion of cast to rolled anodes depends on the com- 
position of the bath, but it may be laid down as a rule that 
baths with greater resistance require more cast anodes, and 
baths with less resistance more rolled anodes. Baths with the 
greatest resistance, for instance, that prepared according to 
formula I, require only cast anodes, while baths with the 
smallest resistance, for instance, those containing ammonium 
chloride, may to advantage work only with rolled anodes ; 
baths with medium resistance require mixed anodes. 

The proper proportion has been established when, after work- 
ing for some time, the original reaction of the bath remains as 
constant as possible. When the bath is observed to become 
alkaline, the number of rolled anodes shpuld be increased, but 
when the content of acid increases they should be decreased, 
and the number of cast anodes increased. 

Cast anodes, especially those not cast veiy hot, have, to be 
sure, the disadvantage of becoming brittle, and crumbling 
before they are entirety consumed. Nickel anodes cast in iron 
moulds are so hard on their surfaces as to resist the action of 
the bath, and dissolve only with difficulty, so that the con- 
tent of metal of the bath is only incompletely replenished. 
Anodes cast in sand moulds, and slowly cooled, are porous 
and consequently dissolve readily, but by reason of their por- 
osity their interior portions are also attacked. If such an 
anode be broken, it will be found that the interior contains a 
black powder (nickel oxide) which novices sometimes believe 
to be carbon. In fact cases have been heard of that customers 
have complained that the anodes furnished them were not 
nickel anodes at all, but simply carbon plates coated with a 
layer of nickel. 

The cast anodes suspended to the ends of the conducting 
18 



274 ELECTRO-DEPOSITION OF METALS. 

rods are especially strongly attacked, and, therefore, when 
rolled and cast anodes are used together, it is best to suspend 
the latter more towards the center, and the former on the ends 
of the rods. 

These drawbacks, however, are not sufficient to prevent 
the use of a combination of cast and rolled anodes when re- 
quired by the composition of the bath. The brittle remnants 
of the anodes are thoroughly washed in hot water, dried, and 
sold. 

Rolled nickel anodes are less liable to corrosion, and may be 
used up to the thickness of a sheet of paper before they fall to 
pieces. It is, however, best to replace them by fresh anodes 
before they become too thin, since with the decrease in thick- 
ness their resistance increases. 

It is best to allow the anodes to remain quietly in the bath > 
even when the latter is not in use, they being in this case not 
attacked. By frequently removing and replacing them they 
are subject to concussion, in consequence of which they 
crumble much more quickly than when remaining quietly in 
the bath. 

In the morning, before nickeling is commenced, the anodes 
will frequently show a reddish tinge, which is generally 
ascribed to a content of copper in the bath or in the anodes. 
This reddish coloration also appears when an analysis shows 
the anodes, as well as the bath, to be absolutely free from cop- 
per. It is very likely due to a small content of cobalt, from 
which nickel anodes can never be entirely freed. It would 
seem that by the action of a feeble current, cobaltous hydrate 
is formed, which, however, immediately disappears on con- 
ducting a strong current through the bath. 

Pfanhauser is of the opinion that this reddish tinge is due 
to a separation of copper. In fact, even the purest brands of 
anodes contain traces of copper, but, on the other hand, the 
nickel salts are at present furnished mostly entirely free from 
copper, and a nickel bath would have to be worked for a long 
time before a content of copper would be transferred to it from 



DEPOSITION OF NICKEL AND COBALT. 275 

the anodes. An experiment showed that a bath prepared 
with nickel salt absolutely free from copper produced a slight 
red film upon a new anode without the current having been 
in action ; a bright steel-sheet served as anode. This does 
not indicate the separation of copper, as its derivation would 
in this case be inexplicable. 

The anodes are supported by pure nickel wire 0.11 to 0.19 
inch thick, or by strips of nickel sheet riveted on. 

It has previously been mentioned that the anodes in baths 
at rest are frequently more strongly attached at the upper than 
at the lower portions, because specifically lighter layers of fluid 
are present on top and heavier ones below, and the current 
takes the road where there is the least resistance. This dis- 
proportionate solution of the anodes may, however, also be 
noticed in baths which are agitated, and consequently in which 
no layers of different specific gravities are present. The lower 
and side edges will be found more corroded than the middle 
portions of the anodes, and the backs opposite to which no 
objects are suspended appear also strongly attacked. These 
observations render plausible Pfanhauser's supposition that the 
current does not in all places migrate directly and in straight 
lines from the anodes to the cathodes, but that, as with the 
magnetic lines of force, this migration takes place in curves, 
especially when the anode-surface is small in proportion to the 
cathode-surface. Pfanhauser has applied the term scattering 
of current lines to this migration of the current in curves, and 
has noticed that it grows with the electrode-distance, and 
decreases as the electro-surfaces are increased. 

Execution of nickeling. Next to the correct composition of 
the bath and the proper selection of the anodes, the success 
of the nickeling process depends on the articles having been 
carefully freed from grease and cleaned, and on the correct 
current-strength. 

The mechanical preparation of the objects has been dis- 
cussed on page 188 et seq. 

The directions for the removal of grease, etc., given on p. 



276 ELECTRO-DEPOSITION OF METALS. 

228, also apply to objects to be nickeled. In executing the 
operations, it should always be borne in mind that though 
dirty, greasy parts become coated with niokel, the deposit im- 
mediately peels off by polishing, because an intimate union 
of the deposit with the basis-metal is effected with only per- 
fectly clean surfaces. Touching the cleansed articles with the 
dry hand or with dirty hands must be strictly avoided ; but, 
if large and heavy objects have to be handled, the hands 
should first be freed from grease by brushing with lime and 
rinsing in water, and be kept wet. 

As previously mentioned, the cleansed objects must not be 
exposed to the air, but immediately placed in the bath, or, if 
this is not practicable, be kept under clean water. 

While copper and its alloys (brass, bronze, tombac, Ger- 
man silver, etc.), as well as iron and steel, are directly nick- 
eled, zinc, tin, Britania and lead are generally first coppered 
or brassed. 

With a suitable composition of the nickel bath and some 
experience, the last-mentioned metals may also be directly 
nickeled ; but, as a rule, previous coppering or brassing is 
preferable, the certainty and beauty of the result being 
thereby considerably enhanced. 

Security against rust. — By many operators it is preferred to 
copper iron and steel articles previous to nickeling, it being 
claimed that by so doing better protection against rust is 
secured. However, comparative experiments have shown 
that with the thin coat of copper which, as a rule, is applied, 
this claim is scarcely tenable, and the conclusion has been 
reached that a thick deposit of nickel obtained from a bath of 
suitable composition protects the iron from rust just as well 
and as long as if it had previously been slightly coppered. 
It cannot be denied that previous coppering of iron articles 
has the advantage that in case the articles have not been 
thoroughly cleansed, the deposit of nickel is less liable to peel 
off, because the alkaline copper bath completes the removal 
of grease ; but with objects carefully cleansed according to the 



DEPOSITION OF NICKEL AND COBALT. 277 

directions given on page 228, previous coppering is not neces- 
sary. 

The case, however, is different if the copper deposit is pro- 
duced in order to act as a cementing agent for two nickel 
deposits. If, for instance, parts which have previously been 
nickeled, and from which the old deposit cannot be removed 
by mechanical means, are to be re-nickeled, coppering is re- 
quired, because the new deposit of nickel adheres very badly 
to the old. Where articles are to be protected as much as 
possible from rust, coppering is advisable, but the best success 
is attained by a method different from the one generall} 7 pur- 
sued. In nickeling, for instance, parts of bicycles which are 
exposed to all kinds of atmospheric influences, they are first 
provided with a thick deposit of nickel, then with a thick coat 
of copper, and finally again nickeled, they thus being twice 
nickeled. It has previously been mentioned that every de- 
posit is formed net-like, the meshes of the net being larger or 
smaller, according to the nature of the metal deposited. If 
now thick la} T ers of two different metals are deposited one on 
the top of the other, the net-lines of one deposit do not con- 
verge into those of the previous deposit, but are deposited be- 
tween them, thus consolidating the net. It will now be readily 
understood that by the subsequent polishing the further con- 
solidation of the deposits will be far more complete than when 
the basis-metal receives but one deposit, which is to be consoli- 
dated by polishing. It is a remarkable fact that the porosity 
of the nickel deposit varies if the article is nickeled in several 
baths of different composition. Thus denser deposits may be 
obtained by suspending the articles in two or three baths, 
which proves that the different resistances of the respective 
baths of one and the same metal exert an influence upon the 
greater or slighter density of the net. 

However, under certain conditions, even iron and steel 
objects doubly nickeled in the above-described manner do not 
offer a sure guarantee against rusting of the basis-metal, and 
to absolutely prevent the latter, the following means may be 
adopted : 



278 ELECTRO-DEPOSITION OF METALS. 

The objects are provided with an electro-deposit of zinc. 
This deposit is scratch-brushed, coppered in the copper cya- 
nide bath, rinsed in water, and finally nickeled, at first with a 
strong current, which is after a few minutes reduced to the 
normal current-density. It is recommended to polish the 
objects thus treated with circular brushes, and not use polish- 
ing wheels which may cause them to become heated, because 
by such heating blisters are readily formed. 

Another plan is as follows : The objects are first coppered 
in the copper cyanide bath. The thickness of this deposit is 
then increased to 0.15 or 0.2 millimeter in the acid copper 
bath (see Galvanoplasty). It is then polished and nickeled. 
Or, if there is sufficient time, a very thick deposit of nickel is 
directly produced upon the object with the use of a cold ethyl 
sulphate nickel bath, or a hot quick nickeling bath (see pp. 
266 et seq.). 

TJie objects should never be suspended in the bath without cur- 
rent, since the baths, with few exceptions, exert a chemical 
action upon many metals, which is injurious to the electro- 
plating process, and especially with nickel baths it is necessary 
to connect the anode-rods and object-rods before suspending 
the objects. 

Over-nickeling. An error is frequently committed in nickel- 
ing with too strong a current, the consequence being that the 
deposit on the lower portions of the objects soon becomes dull 
and gray-black, while the upper portions are not sufficiently 
nickeled. This phenomenon is due to the reduction of nickel 
with a coarse grain in consequence of too powerful a current, 
and is called burning or over-nickeling. A further consequence 
of nickeling with too strong a current is that the deposit 
readily peels off after it reaches a certain thickness. This 
phenomenon is due to the hydrogen being condensed and 
retained by the deposit, which is thereb}'' prevented from 
acquiring greater thickness. 

Especially do those objects suspended on the ends of the 
rods nickel with great ease. This evil can be avoided by 



DEPOSITION OF NICKEL AND COBALT. 279 

hanging on both ends of the rods a strip of copper-sheet about 
0.39 inch wide, and of a length corresponding to the depth of 
the bath. 

Normal deposition. The following criteria may serve for 
judging whether the nickeling progresses with a correct cur- 
rent-strength: In two, or at the utmost three, minutes, all 
portions of the objects must be perceptibly coated with nickel, 
but without a violent evolution of gas on the objects. Small 
gas bubbles rising without violence and with a certain regu- 
larity are an indication of the operation progressing with 
regularity. If, after two or three minutes, the objects show no 
deposit, the current is too weak, and in most cases the objects 
will have acquired dark, discolored tones. In such case, 
either a stronger current must be introduced by means of the 
rheostat, or, if the entire volume of current generated already 
passes into the bath, the object-surface has to be decreased, 
or, if this is not desired, the battery must be strengthened by 
adding more elements, or by fresh filling, etc. 

If, on the other hand, a violent evolution of gas appears on 
the objects, and the latter are well covered in a few seconds, 
and the at first white and lustrous nickeling changes in a few 
minutes to a dull gray, the current is too strong, and must be 
weakened either by the rheostat, or by uncoupling a few 
elements, or diminishing the anode-surface, or finally by 
suspending more objects in the bath. 

These criteria also apply to nickeling with the dynamo. 

The most suitable current- density for nickeling varies very 
much, as will be seen from the preceding explanations. For 
the ordinary cold electrolysis it varies for copper, brass, iron, 
and steel from 0.3 to 1.5 amperes, while zinc, previously cop- 
pered, requires 1 to 1.2 amperes. In the hot nickel bath the 
•current-density may be up to 5 and more amperes. 

In nickeling zinc objects greater current-density and higher 
•electro-motive force are required. If the current is not of suffi- 
cient strength, black streaks and stains are formed, zinc is dis- 
solved, and the nickel bath spoiled. These evils are frequently 



280 ELECTRO-DEPOSITION OF METALS.. 

complained of by nickel-platers who have not a clear percep- 
tion of the prevailing conditions (see polarization-current.) A 
vigorous evolution of gas must take place on the zinc objects, 
otherwise a serviceable deposit will not be obtained. 

In most cases the electro-plater will in a few days learn cor- 
rectly to judge the proper current-strength by the phenomena 
presented by the objects, and if he closely follows the direc- 
tions given but few failures will result. It may here be again 
repeated that the use of a voltmeter and ammeter, as well as- 
of a rheostat, greatly facilitates a correct estimate of the proper 
current-strength, and these instruments should for the sake of 
economy never be omitted in fitting up an electro-plating; 
plant. 

It is in every case advisable first to cover the objects, i. e.,. 
to effect the first deposit of nickel, with the use of a strong- 
current, in order to withdraw the metals from the action of the 
solution. The current is then reduced to a suitable strength 
and nickeling finished with this current. With a current 
thus regulated, the objects may be allowed 1 to remain in the 
bath for hours, and even for days. It is further possible to. 
nickel by weight and attain deposits of considerable thickness. 

If very thick deposits of nickel are to be produced in the 
ordinary bath, the objects must be frequently turned, as the 
lower portions are more heavily nickeled than the upper; fur- 
ther, as soon as the deposit acquires a dull bluish luster, it- 
has to be thoroughly scratch-brushed, in doing which, how- 
ever, the objects must not be allowed to become dry. After 
scratch-brushing it is advisable to cleanse the deposit once 
more with the lime-brush, and after rinsing replace the objects- 
in the bath. If burnt places cannot be brightened and 
smoothed with the scratch-brush, the desired end is readily 
attained with the assistance of emery paper or pumice. 

For solid nickeling it suffices for most articles, with a nor- 
mal current to allow them to remain in the bath until a mat- 
bluish shine appears ; this is an indication that the deposit 
has acquired considerable thickness, provided the bath has- 



DEPOSITION OF NICKEL AND COBALT. 281 

not been alkaline. In alkaline baths this dull deposit is fre- 
quently formed before the deposit has attained considerable 
thickness and this may cause errors, if the reaction of the bath 
is not frequently controlled. 

If the mat appearing objects are permitted to remain longer 
in the bath without scratch-brushing, the mat bluish tone 
soon passes into a mat gray, and all the metal deposited in 
this form must be polished away in order to obtain a bright 
luster. 

Whether the deposit of nickel is sufficiently heavy for all 
ordinary demands is, according to Fontaine, shown by rub- 
bing a nickeled corner or edge of the object rapidly and with 
energetic pressure upon a piece of planed soft wood until it 
becomes hot. The nickeling should bear this friction. This 
test can be recommended as perfectly reliable. 

Faulty arrangement of anodes. If the objects, after having 
been suspended for some time in the bath, are only partially 
nickeled, it is very likely due to the defective arrangement 
of the anodes. This occurs chiefly with large round objects 
and with articles having deep depressions (cups, vases, etc.). 
It is, of course, supposed that the wires to which the objects 
are suspended in the bath have a sufficiently large cross- 
section to carry the current required for nickeling the entire 
surface of the object. 

For flat objects suspending them between two rows of anodes 
suffices. Round objects with a large diameter should be quite 
surrounded with anodes, and be as nearly as possible equi- 
distant from them. This arrangement should especially not 
be neglected where a heavy and uniform deposit of nickel is 
to be applied to round or half-round surfaces, for instance, 
large half-round stereotype plates for revolving presses. 

The arrangement of two object-rods between two anode-rods 
is permissible only for small and thin articles such as safety- 
pins, crochet needles, lead-pencil holders, etc. For articles 
with larger surfaces it is decidedly objectionable, because the 
sides of the articles turned towards the anodes acquire a 



282 ELECTRO-DEPOSITION OB^ METALS. 

thicker deposit than the inside surfaces, and the thickness of 
the deposit decreases with the distance from the anodes. 

Nickeling of cavities and profiled objects. While for smooth 
articles the most suitable distance of the anodes from the 
•objects is 3f to 5f inches, for objects with depressions and 
cavities it must be larger, if it is not preferred to make use 
of the methods described later on. However, a deposit of a 
uniform thickness cannot be obtained by this means, because 
the portions nearer to the anodes will acquire a thicker de- 
posit than the cavities ; hence the use of a small hand anode, 
which is connected by means of a thin, flexible wire with the 
anode-rod, and introduced into the depressions and cavities, is 
to be preferred. This, of course, renders it necessary for a 
workman to stand alongside the bath and execute the opera- 
tion by hand ; but as the small anode can be brought within 
•a few millimeters of the surface of the article, and at this dis- 
tance slowly moved around it, a correspondingly thick deposit 
is in a short time formed. 

At any rate baths in which objects with depressions and 
profiled articles are to be nickeled must possess greater resist- 
ance than baths for nickeling flat articles, and it is inexplica- 
ble why a bath with a large content of ammonium chloride 
and consequently slight conducting resistance can be recom- 
mended, as has been done, for nickeling hollow articles. 
When baths containing ammonium chloride are used for nick- 
eling articles with deep cavities the portions nearest to the 
anodes will frequently be found overnickeled— burnt — before 
the deepest portions are at all covered with nickel, and if the 
•operator waits until the deposit upon the latter portions has 
acquired the desired thickness, the deposit already peels off 
from the former portions, and frequently before that time. By 
•comparative experiments in nickeling the inside of brass tubes, 
15 millimeters in diameter, it was found that in a bath with great 
resistance, as well as in one with slight resistance, nickeling 
was equally well effected. However, the phenomenon of peel- 
ing off, above referred to, appeared in the bath which contained 



DEPOSITION OP NICKEL AND COBALT. 283 

ammonium chloride when the ends of the 120-millimeter long 
tubes turned away from the anode were still so slightly nick- 
eled that the basis-metal showed through. On the other 
hand, in the bath without ammonium chloride the end of the 
tube turned towards the anode, to be sure, became mat, but 
did not peel off in polishing, and nickeling in the interior of 
the tube had progressed well to the opposite end, the basis- 
metal there being well covered. 

In nickeling lamp-feet of cast-zinc, the use of the hand- 
anode can scarcely be avoided if the depressed portions also 
are to be provided with a uniformly good deposit. Moreover, 
zinc articles form an exception to the general rule in so far as 
by reason of the highly positive properties of zinc, the resist- 
ance of the bath may be slighter than the baths for nickeling 
copper and its alloys, as well as iron and steel. 

Besides the above-mentioned general rules for nickeling, 
which also hold good for other electro-plating purposes, the 
following may be given : 

In suspending the objects in the bath, rub the metallic 
hooks or wires, with which they are secured to the rods, a few 
times to and fro upon the rod, in order to be sure that the 
place of contact is purely metallic. It is also well to acquire 
the habit of striking the rod a gentle blow with the finger 
every time when suspending an object, the gas-bubbles settling 
on the articles becoming thereby detached and rising to the 
surface. It is further advisable, before securing the objects to 
the object-rod, to move them up and down several times ; so 
to say, shake them beneath the fluid, whereby, on the one 
hand, the layers poorer in metal are mixed with those richer 
in metal, and, on the other, any dust which may float upon 
the bath and settle on the objects is removed. 

The objects suspended in the bath should not touch one 
another, nor one surface cover another, and thus withdraw it 
from the direct action of the anode. In the first case stains 
will readily form on the places of contact, and, in the latter, 
the covered surface acquires only a slight deposit. That the 
objects must not touch the anodes need scarcely be mentioned. 



284 ELECTRO DEPOSITION OF METALS. 

Objects with depressions and cavities should be suspended 
in the bath so that the air in the depressions and cavities can 
escape, which is effected b} 7 turning the depression upwards, 
or, if there are several depressions on opposite sides, by turn- 
ing the articles about after being introduced into the bath. 
Air-bubbles remaining in the hollows prevent contact with 
the solution, no deposit being formed on such places. 

Polarization. It remains to say a few words in regard to the 
so-called polarization phenomena. In the theoretical part of 
this work, it has been shown that by dipping two plates of 
different metals in a fluid a counter or polarization current is 
generated, which is the stronger the greater the difference in 
the potentials of the two metals in the solution is. If the 
anodes in a nickel bath consist of nickel and the objects of 
copper, the counter-current will be slight. It becomes, how- 
ever, greater when iron objects are suspended in' the bath, and 
still greater with zinc surfaces which are to be nickeled, be- 
cause with the solutions here in question, zinc possesses towards 
nickel an essentially higher potential. Now, since the counter- 
current flows in a direction opposite to that of the current 
introduced at the bath, the latter is weakened, and the more 
so the stronger the counter-current is. This explains why 
iron requires a stronger current for nickeling than copper- 
alloys, and zinc a stronger one than iron. 

Now it may happen that the counter-current becomes so 
strong as to entirely check the effect of the main current, and 
even to reverse the latter, the consequence being that, in the 
first case, the formation of the deposit is interrupted, and, in 
the latter, that the deposit is again destroyed, and the metals 
of which the articles consist dissolve and contaminate and 
spoil the bath. To avoid this, a main current must be con- 
ducted into the bath, which, by its sufficiently, large electro- 
motive force can overcome the counter-current, and the con- 
sequences of the reversal of the current can be prevented by 
using the galvanometer and observing the deflection of its- 
needle, which (according to p. 143) in proper time indicates 



DEPOSITION OF NICKEL AND COBALT. 285 

the appearance of a reversed current. Now if a nickel-plater 
has only a slight current at his disposal, it follows from the 
above explanation that, before nickeling the more electro- 
positive metals, such as iron, tin, zinc, it is best first to copper 
them, and thereby overcome the action of these metallic 
surfaces as regards the formation of the counter-current. 

It happens comparatively seldom that the counter-current 
becomes so strong as to destroy the deposits formed, because 
for nickeling powerful , Bunsen cells with two acids, or a 
dynamo with at least 4 volts' impressed electro-motive force, 
are generally used. It is, however, well to acquaint the oper- 
ator with all possible contingencies, and to explain the reason 
why the articles are preferably covered with a strong current. 
Sprague recommends an initial current of 5 volts' electro- 
motive force, but in most cases one of 3.5 volts suffices for 
nickeling iron and copper alloys. 

Stripping defective nickel. Defective nickeling must, as a 
rule, be completely removed before the objects can be nick- 
eled, since the second deposit does not adhere to the previous 
•one, but frequently peels off in polishing or by slightly bend- 
ing the object. The reasons for this behavior are : 1. Like 
iron, nickel readily oxidizes on the surface, but this oxidation 
is not so heavy as to be perceptible. Previous to nickeling 
this oxide has not been completely removed and in the case 
of quite old plated objects the nickel has had a chance to 
oxidize. Nickel, however, adheres firmly only to metallic 
nickel and not to the oxide ; hence the second deposit peels 
•off. 2. In case the deposit is comparatively new and has not 
been exposed for some time to the action of atmospheric air, 
the peeling off of nickel deposited upon nickel is, as a rule, 
caused by the polishing material remaining upon the surface. 
Vienna lime and similar agents which contain paraffin and 
other mineral fats and wax are much used for polishing 
nickel. These substances partially penetrate into the pores of 
the deposited nickel or remain upon the surface. By the 
ordinary means of cleaning the mineral fats or wax are not 



286 ELECTRO-DEPOSITION OF METALS. 

removed, the consequence being that the second deposit of 
nickel does not adhere. With the use of animal fats, which 
readily saponify, as polishing agents, the case is not so bad, 
but even under these conditions, the nickel has a tendency to 
peel off. It must be borne in mind that as previously men- 
tioned, all electrolytically produced deposits are composed of a 
net- work of ver}' minute crystals, the deposit being thus of a 
porous nature. In polishing larger or smaller quantities of 
the polishing agent penetrate into these pores, and their com- 
plete removal is a very difficult matter. 

For the removal of the nickel coating the following strip- 
ping acid, which may be used either cold or tepid, has been 
recommended : Sulphuric acid of 66° Be., 4 lbs. ; nitric acid 
of 40° Be., 1 lb. ; water about 1 pint. First put the water in 
a stoneware jar and cautiously add, a little at a time, the sul- 
phuric acid, since considerable heat is generated when this 
acid is mixed with water. When the entire quantity of sul- 
phuric acid has been added, pour in the nitric acid, when the 
bath is ready for use. In making up the stripping bath, the 
proportions of the acids may be varied, but the foregoing will 
be found to answer every purpose. An addition of 8 ozs. of 
potassium nitrate to the bath has also been recommended. 

When stripping nickel-plated articles in the above bath it is 
necessary to watch the operation attentively, since some arti- 
cles are very lightly coated and a momentary dip is frequently 
sufficient to deprive them of their nickel. Other articles which 
have been thoroughly well nickeled, but require from some 
accidental cause to be stripped and re-nickeled, will need im- 
mersion for several minutes ; indeed well nickeled articles may 
occupy nearly half an hour in stripping before the underlying 
surface is entirely bare. The operation of stripping should be 
conducted in the open air, or in a fire-place, so that the acid 
fumes, which are very pernicious, can escape freely. The 
articles should be attached to a stout copper wire, and after a 
few moments' immersion should be removed from the bath to 
see how the operation progresses, it being absolutely necessary 



DEPOSITION OF NICKEL AND COBALT. 287 

that the work should not remain in the stripping solution one 
instant after the nickel is removed. The object is then trans- 
ferred to a large volume of cold water, and after washing twice 
or three times in fresh water is ready for the subsequent stages 
of the process. When stripping has been properly effected, 
the underlying metal exhibits a bright, smooth surface, giving 
little evidence of the mixture having acted upon it. 

Many platers, however, prefer to remove the nickel coating 
mechanically by brushing with emery. From depressions it 
is as much as possible removed with the brush, after which the 
object is freed from grease and pickled, and coppered before 
nickeling. In this case the layer of copper serves for cement- 
ing together the old and new deposits, and there will be no 
danger of the new deposit peeling off in polishing. 

It has also been proposed to strip by electrolysis by making 
the object the anode in an old nickel bath, Attention is 
equally necessary in conducting this process to guard against 
any attack upon the basis-metal ; but since it is impossible to 
prevent all action, no bath which is to be afterward employed 
for depositing the metal should be used for this purpose, as it 
will become gradually charged with impurities. A 10 per 
cent, solution of sulphuric acid in water may be equally 
readily adapted to the electrolytic stripping. 

Many nickel-plated iron and steel objects are so cheap that 
it does not pay to strip the nickel from them, and it is best to 
throw them on the scrap pile. In some cases, however, for 
instance, surgical instruments, fire-arms, fine cutlery and 
other more expensive articles, it is frequently desirable to re- 
move the old nickel deposit. To be sure, nitric acid would 
remove the nickel, but it also attacks iron and steel and 
causes pitting. For stripping such articles by electrolysis the 
following bath has been recommended : Water 1 lb., potas- 
sium cyanide 1.8 ozs., yellow prussiate of potash 0.5 oz. The 
iron or steel object to be stripped is suspended as anode in the 
bath, which should be used at a temperature of 122° F. A 
sheet of iron or steel serves as cathode. For stripping a thin 



288 ELECTRO-DEPOSITION OF METALS. 

deposit only a few hours are required, but a whole day for 
thick deposits. However, the operation requires no special 
attention, as the iron or steel surface is not attacked and there 
is no danger of pitting. The current-strength should be the 
same as usually employed for nickel-plating. 

As a remedy against the yellowish tone of the nickeling, 
Pfanhauser recommends suspending the nickeled, articles, im- 
mediately after taking them from the nickel bath, as anodes 
in a nickel bath acidulated with citric or hydrochloric acid, a 
piece of sheet nickel serving as the cathode, and to allow the 
current to act for a few seconds. It is claimed that thereby 
the basic nickel salts separated together with the nickel, and 
to which, according to Pfanhauser, the yellowish tinge is due, 
are dissolved, and the nickeling will show a pure white tone. 

As nickel anodes contain, as a rule, iron, a minute quantity 
of this metal is deposited together with the nickel, and the 
latter is inclined to form a mat surface or to tarnish. If the 
objects are to be polished this does not matter, but if they are 
not to be polished slight mat stains frequently appear upon 
the surface after drying. Such stains can be removed by the 
use of a bath of dilute hydrochloric acid (2 parts water, 1 part 
acid). After thoroughly rinsing the object in water, immerse 
it for a moment in the acid bath, and then rinse again care- 
fully. Now, without drying, draw the object through a soap- 
bath and rinse again. Since the soap solution leaves a thin 
film of oil upon the nickel surface not much water will adhere 
to it, and it will quickly dry. It will be found that the mat 
spots have disappeared or the stains are scarcely perceptible. 

Defective nickeling. The following is a brief resume of the 
principal defects which may occur in nickeling, as well as the 
means of avoiding them : 

1. The articles do not become coated with nickel, but 
acquire discolored, generally darker, tones. Reason : The 
current is either too feeble to effect the reduction of nickel, 
and the coloration is due to the chemical action of the nickel 
solution upon the metals constituting the objects. This phe- 



DEPOSITION OF NICKEL AND COBALT. 289 

nomenon is frequently observed in nickeling zinc articles. 
Remedy : Increase the current or diminish the area of sus- 
pended objects ; also examine whether the current actually 
passes into the bath, otherwise clean the places of contact. 

2. A deposition of nickel takes place, but it is dark or 
spotted or marbled, even with a sufficiently strong current. 
Reasons : The bath is either alkaline, which has to be ascer- 
tained by testing with litmus-paper, and, if so, the slightly 
acid reaction of the bath has to be restored by the addition of 
•a suitable acid ; or, the bath is too concentrated, in which 
•case a separation of crystals will be observed — this is remedied 
by diluting with water ; or, the nickel solution is very poor in 
metal, which can be remedied by the addition of nickel salt ; 
it should also be tested as to the admixture of copper, the 
production of dark tones being frequently due to this— in this 
case the bath is allowed to work for some time, and if the 
content of copper is inconsiderable a white deposit will soon 
be obtained ; or, the cleaning and pickling of the articles have 
not been thoroughly done, which is remedied by again clean- 
ing them ; or, the conducting power of the bath is insufficient, 
which is remedied by the addition of a suitable conducting 
salt. 

When freshly prepared baths yield dark nickeling, it can 
generally be remedied by working the bath two or three 
hours, if it is not over-concentrated and the cause, as above 
mentioned, has to be looked for in a small content of copper 
in the nickel salt. 

3. A yellowish tinge of the nickeling. Reason: Alkalinity 
•of the bath. Remedy : See under 2 ; or, with cast-iron, an 
insufficient metallic surface, which is remedied by repeating 
the scratch-brushing ; or, unsuitable composition of the bath. 

4. The objects rapidly acquire a white deposit of nickel, 
but the color soon changes to a dull gray-black, especially on 
the lower edges and corners. Reason : Too strong a current. 
Remedies : Regulating the current, or suspending more objects, 
•or uncoupling elements. Frequent turning of the articles. 

19 



290 ELECTRO-DEPOSITION OF METALS. 

5. The nickeling is white, but readily peels off by scratching 
with the finger-nail, or by the action of the polishing wheel. 
Reasons: The current is too strong, which is remedied as under 
4 ; or, the bath is too acid — this is remedied by the addition of 
ammonia, potassium carbonate, or nickel carbonate, according 
to the composition of the bath; or, freshly prepared nickel bath 
or freshly made additions, this being remedied by working the 
bath and by very careful regulation of the current in nickeling 
during the first days ; or, insufficient cleaning and pickling, 
which is remedied by thorough cleaning after removing the de- 
fective deposit, or, if it cannot be entirely removed, coppering. 

6. Though nickeling may proceed in a regular manner, 
some places remain free from deposit. Reasons: Either the 
surfaces of some of the objects touch one another ; or, are- 
stained by having been touched with dirty fingers ; or, air 
bubbles are inclosed in cavities. Remedy: Removal of the- 
causes. 

7. The deposit appears with small holes. Reason: A de- 
posit of particles of dust upon the objects. Remedy : Remove 
the dust from the surface. When there is a general turbidity 
of the bath in consequence of alkalinity, add the most suitable- 
acid, and boil and filter the bath; or, insufficient removal of gas- 
bubbles from the objects. Remedy: Shake the object-rods by 
blows with the finger. 

8. Deposition takes place promptly upon the portions of 
the objects next to the anodes, while deeper portions remain 
free from nickel or become black. Reason: Too slight a 
distance of the objects from the anodes. Remedy : Increasing 
the distance ; with large depressions, treatment with the hand- 
anode. 

Refreshing nickel baths. — According to their composition, 
the amount of work performed, and the anodes used, the baths 
will in a shorter or longer time require certain additions in 
order to keep their action constant. By " refreshing " is not 
understood the small addition of acid or alkali from time to- 
time required for restoring the original reaction of the baths,. 



DEPOSITION OF NICKEL AND COBALT. 291 

but additions intended to increase the metallic content and 
the diminished conductivity. 

The metallic content is increased by boiling the bath with 
some of the nickel salt used in its preparation, while the con- 
ductivit}'- is improved by adding, at the same time, so much 
conducting salt as is necessary to restore the electro-motive 
force originally required. Nothing definite can, of course, be 
said in regard to the quantity of such additions, it being ad- 
visable to observe their effect on a small portion of the bath, 
so as to be sure not to spoil the entire bath. 

Nickel baths bear, as a rule, refreshing several times, but 
as in the course of time they take up impurities, even when 
the greatest care is exercised, it is best to refresh them at the 
utmost twice, and then to renew them entirely. 

The treatment of the articles after nickeling, as well as after 
all electro-plating processes, has already been described, and 
it is only necessary here to refer again to the fact, that with 
articles of iron and steel, immersion in boiling water before 
drying in sawdust is absolutely necessary, and subsequent 
drying in a drying chamber is also a great safeguard as 
regards stability and protection against rust. 

Nickel deposits are polished upon felt wheels or bobs of cloth, 
muslin or flannel, with the use of Vienna lime, rouge, Victor 
white polish, etc. (See "Polishing," p. 216). To give the 
objects the highest luster possible, it is advisable finally to 
polish them upon a woolen brush with dry Vienna lime. 

Sharp edges, corners and raised portions should be held 
only with slight pressure against the polishing wheels, they 
being more strongly attacked by them than flat surfaces. The 
latter can stand a stronger pressure without fear of cutting 
through the deposit, provided the latter is of sufficient thick- 
ness and hardness. 

Knife blades and surgical instruments with sharp edges 
require special care in polishing, which will later on be re- 
ferred to. 

Cleansing polished objects. After polishing, the nickeled 



292 ELECTRO-DEPOSITION OF METALS. 

objects, especially those with depressions, have to be freed 
from polishing dirt by brushing with hot soap-water, or dilute 
hot caustic lye, or benzine, then rinsed in hot water and dried. 

Calculation of the nickeling operation. Many inquiries re- 
garding the mode of calculating the price to be charged for 
nickeling objects give rise to the following remarks : If the 
same article with the same definite surface is always to be 
nickeled, the calculation is quite simple. From the current- 
strength and the time required for nickeling, the weight of 
the nickel-deposit can be readily determined by keeping in view 
that 1 ampere theoretically deposits in 1 hour 1.1 gramme 
of nickel, or about 1 gramme if the current output be taken 
into consideration. The value of the ascertained weight has 
to be determined by taking the cost of the anodes as the basis, 
and from this is calculated the constant price of the separate 
piece. To this has to be added the wages for grinding, pol- 
ishing and nickeling, as well as the amount of power required, 
which, according to the motors in use, has to be established 
by a special calculation ; further, the materials used for grind- 
ing, polishing, freeing from grease, etc., and a certain profit. 
However, in most cases it is scarcely possible to make such 
detailed calculations in electro-plating establishments in which 
the most diverse objects have to be nickeled, because, on the 
one hand, the determination of the surface of the separate 
objects would be difficult and time-consuming, and on the 
other, it would be very troublesome, in consequence of the 
change of the object-surfaces in the bath, to keep an accurate 
account of the current-strength and time required for the 
separate objects. 

To attain the object, it has in practice proved the simplest 
plan to take as a basis the wages paid to the grinder and 
polisher, and multiply them by 4, in order to obtain the sell- 
ring price of the work furnished. The selling value thus deter- 
>mined includes all expenses and a fair profit. Somewhat more 
will have to be allowed for particularly complicated objects , 
which require assistance with the hand-anode. This mode of 



DEPOSITION OF NICKEL AND COBALT. 



293 



calculation has on the whole been found to answer for solid, 
heavy nickeling. For light nickeling — coloring white in the 
nickel bath — the selling value might be too high. An extra 
charge will of course have to be made for repairing articles 
which are received for nickeling. 

When objects already ground and polished are sent in to be 
nickeled, the above-mentioned mode of calculation is of course 
not applicable. In that case it has to be calculated how much 
a charge of a bath must bring, in order to cover expenses and 
a certain profit, and from that the approximate selling value 
of the nickeling work may be determined. 

Nickeling small and cheap objects in large quantities. This is 

Fig 114. 




effected by stringing the objects, if feasible, upon a copper wire, 
and placing a large glass bead between every two objects, to 
prevent the surfaces from sticking together in the bath. Such 
objects being generally only slightly nickeled, it suffices to 
allow them to remain for a few minutes only in the bath with 
a strong current, it being advisable to diligently shake the 
bundles in order to effect a change of position of the objects 



294 ELECTRO-DEPOSITION OF METALS. 

and prevent their touching one another, notwithstanding the 
glass bead placed between them. 

Very small objects, such as rivets, pins, etc., which cannot be 
strung upon wire, are nickeled in dipping baskets of stoneware 
or wire. To the bottom of the dipping basket is secured a 
copper or brass wire, which is connected with the object-rod, 
and the articles, not too many at a time, are then placed in 
the basket. During the operation the articles must be con- 
stantly shaken, and as nickel baths, as a rule, do not conduct 
sufficiently well to properly nickel the objects in the basket, 
it is advisable to hold with one hand an anode, connected by 
a flexible wire with the anode-rod, in the basket, while the 
other hand holds the basket (Fig. 114) and constantly shakes 

Fig. 115. 




and turns it. For nickeling in the dipping basket it is further 
advisable to heat the nickel bath. 

In place of a stoneware dipping basket, a basket tray of 
brass wire, Fig. 115, to which are soldered two copper wires 
for suspending it to the object-rod, may preferably be used. 
From the soldered places a few copper wires extend to the 
bottom of the basket. To prevent the basket from becoming 
covered with nickel it is coated with asphalt varnish. At a 
distance of about 1\ to 3 inches below the basket an anode is 
arranged in horizontal position, while with one hand a hand- 
anode is held over the small articles in the basket. By this 
arrangement a thicker deposit is more rapidly obtained, 
especially if, with the other hand, the articles are constantly 
stirred by means of a glass or wooden rod. 



DEPOSITION OF NICKEL AND COBALT. 295 

Warren has described a solution of nickel and one of cobalt 
which can be decomposed in a simple cell apparatus. With 
the nickel solution,~which was prepared by dissolving 100 
parts by weight of nickel chloride in as little water as possible 
and mixing with a concentrated solution of 500 parts of 
Rochelle salts, no satisfactory results could be obtained. The 
cobalt solution however yielded good results, and would seem 
to be suitable for electro-plating small objects in large quan- 
tities. It will be further referred to under " Deposition of 
Cobalt." 

In the last few years a number of contrivances for electro- 
plating small articles in large quantities have been patented, 
the articles to be plated being, as a rule, contained in a revolv- 
ing perforated drum. The drums of some of the contrivances 
are constructed of non-conducting material so that the articles 
receive the current through copper or other metallic strips, 
which are secured in the inside walls of the drums, and are 
brought in various ways in contact with the source of current. 
In other contrivances, for instance, the apparatus of Smith & 
Deakin, metallic pins capable of being turned around the 
shaft, which is in contact with the negative pole of the source 
of current, reach to the layer of articles in the drum, and 
■effect the re-transmission of the current. Since in the con- 
trivances mentioned the anodes are placed outside of the 
•drum, and the latter acts as a diaphragm with great resist- 
ance, a very high electro-motive force is required for the pro- 
duction of the deposit, independent of the fact that the articles 
being in constant motion already require an essentially higher 
electro-motive force. 

In another class of apparatus, the six or eight-cornered drum 
is constructed of the same metal which is to be deposited. 
Every metal plate forming one side is insulated from the next 
plate. The plates which, while the drum is revolving, occupy 
the lowest position and upon which the articles for the time 
being rest, are brought into contact with the negative pole of 
the source of current by a commutator of special construction, 



296 



ELECTRO-DEPOSITION OP METALS. 



while the positive current is carried to the plates occupying a 
higher position, they thus acting as anodes. In this type of 
apparatus the high resistance due to the arrangement of the 
anodes on the outside is overcome, but the commutator with 
the sliding contact constitutes a very sensitive part of the 
construction. 

Fig. 116 shows a mechanical electro-plating apparatus 
patented and manufactured by The Hanson and Van Winkle 
Co., Newark, N. J. The apparatus complete consists of an 

Fig. 116. 




outer wooden tank for containing the solution, a perforated 
revolving plating barrel, made of wood or celluloid in which 
to hold and tumble the work while deposition is going on, 
and necessary rods and connections. The size of the perfora- 
tions required in the plating barrel depends on the class and 
shape of the work to be plated. The perforations should be 
as large as possible without allowing the work to slip through 
or catch in them. The barrel is entirely submerged, thus 
permitting a much larger quantity of work in each batch. 



DEPOSITION OF NICKEL AND COBALT. 



297 



The drive is from the outside, thus avoiding the use of belts 
running in the solution. The barrel is removable at any- 
time without throwing off the belt or interfering with the 
drive. For raising and lowering the plating barrel a lifting 
device is very convenient. Fig. 117 shows a hand-wheel lift- 
ing device. In operation it raises and lowers the plating bar- 
rel in a perpendicular direction, and when the barrel is sus- 
pended above the tank for a few seconds will allow the 

Fig. 117. 






solution to drip directly back into the tank. This reduces 
the loss of solution to a minimum and overcomes the difficulty 
of a wet and sloppy floor. 

In connection with this apparatus the use of patent curved 
elliptic anodes, as shown in the illustration, is recommended. 
The anode is curved to fit the periphery of the revolving bar- 
rel, and when an anode is hung on each side of the tank, the 
barrel holding the work is equidistant at all times from the- 



'298 ELECTRO-DEPOSITION OF METALS. 

-anode ; hence a regular and even deposit is obtained. These 
anodes are cast in all metals with square copper hooks 
attached. 

The above-described mechanical electro-plating devices are 
equally well adapted for zincking articles in large quantities, 
such as screws, nails, rivets, etc., as well as for brassing, 
coppering, etc. 

Nickeling sheet-zinc. The nickeling of sheet-zinc has been 
surrounded with a great deal of mystery by those engaged in 
its manufacture, which may, perhaps, be excusable on the 
ground that there is scarcely another branch of the electro- 
plating industry in which experience had to be acquired at the 
sacrifice of so much money and time as in this. Nevertheless, 
the nickeling of sheet-zinc makes no greater demand on the 
intelligence of the operator than any other electro-plating pro- 
cess, it requiring only an accurate consideration of the relations 
of the electric behavior of zinc towards nickel ; consequently, 
a knowledge of the strength of the counter-current and of the 
chemical behavior of zinc towards the nickel solution, which 
may readily dissolve the zinc ; further, a correct estimation of 
the proper current-strength required for a determined zinc 
surface, as well as of the proper anode surface, and the most 
suitable composition and treatment of the nickel baths. 

With due observation of these conditions, the nickeling of 
sheet-zinc is accomplished as readily as that of other metals ; 
and the suggestions to first cover the sheets in a bath with a 
strong current, and finish nickeling with a weaker current, 
or to amalgamate the zinc before nickeling, need not be 
considered. 

Below the conditions required for nickeling sheet-zinc, and 
the execution of the process itself, together with the pre- 
liminary and final polishing of the sheets, will be found fully 
described. 

The preliminary grinding or polishing is effected upon 
broad cloth wheels (buffs) formed of separate pieces of cloth. 
The polishing lathes run with their points in movable bear- 



DEPOSITION OF NICKEL AND COBALT. 



299 



ings secured in a hanging cast-iron frame by a set screw and 
safety keys, or preferably as shown in Fig. 101, since with 
this construction an injury to the grinder by the lathe jump- 
ing out is impossible. 

The bobs, when new, have on an average a diameter of 12 
to 16 inches, and a. width of 5f to 8 inches. The principal 
point in the construction of these bobs is uniform weight on all 
•sides, quiet running and the possibility of a good polish without 
great exertion depending on this. Bobs not well balanced run 
unsteadil} 7 and jump, thereby producing fine scratches upon 
the sheet. The bobs are constructed as follows: A square piece 
of cloth if folded fourfold and the closed point cut off with a 
pair of scissors, so that on unfolding the cloth, the hole pro- 
duced by the cut is exactly in the center of the cloth disk. 
According to the diameter of the spindle more or less is cut 
away, but in every case just sufficient for the piece of cloth 
to be conveniently pushed upon the spindle. The latter 
which is provided with a pulley and a hoop against which 
the pieces of cloth fix themselves, as well as with a nut 
and screw for securing them, is vertically fastened in a 
vise, and the separate pieces of cloth are pushed upon it 
so that the second piece placed in position forms an angle 
of about 30° (Fig. 118) with the first, the operation being 
thus continued until the bob has the desired width. Next a 
small, but very strong iron disk is laid upon the cloth bob, and 
the separate pieces are pressed together as 
firmly as possible with the screw. The 
spindle is then placed in the bearings, 
and after adjusting the belt upon the 
pulley the bob is revolved, a sharp knife 
being held against it to remove the pro- 
jecting corners. In polishing sheet-zinc 
the bobs make 2,200 to 2,500 revolutions 
per minute, according to whether finely 
rolled or rougher sheets are to be polished. 

For the purpose of preparatory polishing, the operator 



Fig. 118. 




300 ELECTRO-DEPOSITION OF METALS. 

places the sheet upon a support of hard wood of the same size 
and form as the sheet, and grasps the two corners of the sheet 
nearest to his body, together with the support, with the hands, 
applying with the balls of the hands the necessary pressure to 
hold the sheet upon the support. The lower half of the sheet,, 
that furthest from the body, rests upon the knees of the opera- 
tor, and with them he presses the sheet against the polishing 
wheel, constantly moving at the same time, and at not too 
slow a rate, the knees from the right to the left, then from the- 
left to the right, and so on. Previous to polishing, a streak 
of oil about two inches wide is applied by means of a brush 
to the center of the sheet in the visual line of the operator,, 
and the revolving bob is impregnated with Vienna lime by 
holding a large piece of it against it, when polishing of the 
lower portion of the sheet begins. When about f of the sur- 
face has thus been polished, the sheet is turned round and the 
remaining portion subjected to the same process. The sheet 
is then closely inspected to see whether there are still dirty or 
dull places, and, if such be the case, it is polished once more, 
after moistening it with some oil and again impregnating the 
bob with Vienna lime. The sheet being sufficiently polished r 
the oil and polishing dirt are removed by dry polishing, after- 
providing the bob with sufficient Vienna lime, so that the- 
sheets when finished show no streaks of dirt or oil. 

Sheets 50x50, 100x50, and also 150x50 centimeters, can 
in this manner be readily polished, but it is a difficult feat, 
mostly subject to the risk of producing bent places, to polish 
sheets 6 feet long upon the knees. Numerous attempts have 
therefore been made to construct automatic machines for con- 
veniently polishing sheets 12 or more feet long. 

Several such automatic polishing machines have been de- 
scribed and illustrated in the fifth edition of this book, but, 
while they furnish a quite good polish, they have, on the one 
hand, the drawback that thin sheets are readily creased or 
wound around the polishing roll, and, on the other hand, that 
the sheets are with great violence thrown out by the polishing 



DEPOSITION OF NICKEL AND COBALT. 301 

roll if this is not prevented by placing another sheet over a 
portion of the sheet to be polished, and passing it together 
with the latter under the roll. This, however, has the draw- 
back that the covered portion of the first sheet is not polished, 
and has to be again passed under the polishing roll, and the 
place where the edge of the second sheet has rested upon the 
first sheet shows a mark formed by pressure, which, as a rule, 
is not desirable. 

The polishing machine constructed according to the patent 
of Hille and Muller * avoids the above-mentioned drawbacks 
by obliquely standing polishing rolls. In KorHer's f construc- 
tion two polishing rolls move in opposite directions. The 
•sheets are pressed against the rolls by an oscillating table so 
that first one and then the other portion of the table is alter- 
nately advanced towards the corresponding polishing roll. 

In the construction patented by Dr. Langbein & Co., the 
drawbacks of throwing out and crumpling the sheets is over- 
come by the arrangement of two polishing bobs, which alter- 
nately stand still and revolve, however, in opposite directions. 
The table consists of two movable halves ; while one of the 
halves, in an elevated position, presses the sheet carried by the 
transport-rolls against the revolving polishing bob, the other 
half is lowered and its polishing bob remains stationary. 
When a certain length of the sheet has been polished the 
•second polishing bob revolving in an opposite direction is put 
in action, a constant stretching of the sheet being thereby 
effected. 

Freeing zinc sheets from grease. This is best effected in two 
operations, first dry and then wet. For the dry process use a 
very soft piece of cloth and, after dipping it in Vienna lime, 
very finely pulverized and passed through a hair sieve, rub 
•over the sheet in the direction of a right angle to the polishing 
streaks, applying a very gentle pressure. For the wet process, 
•dip a moist piece of cloth, or a soft sponge free from sand, into 

" * German patent, 49736. t German patent, 89648. 



302 ELECTRO-DEPOSITION OF METALS. 

a paste of impalpable Vienna lime, whiting and water, and go 
carefully over the sheet so that no place remains untouched. 
Then rinse the sheet under a powerful jet of water, best under 
a rose, being particularly careful to remove all the lime, going 
over the sheet, if necessary, with a soft, wet rag, and observ- 
ing whether all parts appear evenly moistened. If such be 
the case, cleaning is complete, otherwise the sheet has to be 
once more treated with lime. 

If the sheets are to be nickeled on only one side, two of them 
are placed together with their unpolished sides and fastened on 
the two upper corners with binding screws to which is soldered 
a copper strip about 0.39 inch wide, by which they are sus- 
pended to the conducting rods. Plating is then at once pro- 
ceeded with, without allowing the sheets to remain exposed 
to the air longer than is absolutely necessary. Special care 
must be had that the lime does not dry, as this would produce 
stains. 

With sheets 50 x 50 centimeters, two binding screws suffice 
for suspending the sheets to the conducting rods. With sheets 
100 centimeters long, three binding screws are generally used, 
with sheets 150 centimeters long, five, and with lengths of 
200 centimeters, six or more, so that the current required for 
nickeling finds a sufficient cross-section. 

Some manufacturers nickel the cleansed sheet without pre- 
vious coppering or brassing, and claim special advantages for 
such direct nickeling. This may be done with a bath of nickel 
sulphate and potassium citrate without, or with a greater or 
smaller, addition of ammonium chloride, according to the 
surface to be nickeled and the intensity of current at disposal. 
However, sheet-zinc directly nickeled does not show the warm, 
full tone of sheets previously coppered or brassed ; besides, 
direct nickeling requires a far more powerful current, so that 
it is not even more economical. 

For the nickeling process itself, it is indifferent whether the 
sheets are previously coppered or brassed, but the choice be- 
tween the two is controlled by a few features which must be 



DEPOSITION OP NICKEL AND COBALT. 303 

mentioned. The nickel deposit upon brassed sheets shows a 
decidedly whiter tone than that upon coppered sheets, and 
brassing would deserve the preference if this process did not 
require extraordinarily great care in the ^proper treatment of 
the bath, the nickel deposit readily peeling off, generally in the 
bath itself, which seldom or never occurs with coppered sheet, 
and then may generally be considered due to insufficient 
cleaning or other defective manipulation. 

This peeling-off of the nickel deposit may be prevented by 
giving due consideration to the conditions and avoiding, on the 
one hand, too large an excess of potassium cyanide in the brass 
bath, and, on the other, by regulating the current so that no 
pale yellow or greenish brass is precipitated. Since nickeling 
with a strong current requires only a few minutes for a deposit 
of sufficient thickness capable of bearing polishing, it is gener- 
ally desired to brass the sheets at the same time, so that the 
operation may proceed rapidly and continuously. To do this, 
a very powerful current has to be conducted into the brass bath, 
the result being that a deposit with a larger content of zinc 
and a correspondingly lighter color is formed, but also with a 
coarser, less adherent structure, and this is the principal reason 
why the nickel deposit, together with the brass deposit, peels 
off. To avoid this, the brassing must be done with a current 
so regulated that the deposit precipitates uniformly, adheres 
firmly, and is not porous; the correct progress of the operation 
is recognized by the color being more like tombac, and not 
pale yellow or greenish. When brassing has to be done quickly 
the content of copper in the brass bath must be increased to 
such an extent that a powerful current produces a deposit of 
the above-mentioned color, and, hence, too large an excess of 
potassium cyanide must be strictly avoided. 

It will be seen that brassing requires a certain attention 
which is not necessary in coppering, and therefore the latter 
is to be preferred. 

For coppering, one of the baths, formulas III to VII, given 
under " Deposition of Copper" can be used, to which, for this 



304 ELECTRO-DEPOSITION OF METALS. 

special purpose, more potassium cyanide may be added. The 
sheets should remain in this bath no longer than required to 
uniformly coat them with a beautiful red layer of copper, and 
under no circumstances must they be allowed to remain until 
the coppering commences to become dull or even discolored. 
They should come from the bath with a full, or at least half, 
luster. 

When taken from the copper bath the sheets are thoroughly 
rinsed in a large water reservoir, the contents of which must 
be frequently renewed, care being had to remove any copper 
solution adhering to the unpolished sides which are not to be 
nickeled, since that would soon spoil the nickel bath. The 
sheets are then immediately brought into the nickel bath, it 
being best to suspend two, three, or four of them at the same 
time, to prevent one from being more thickly nickeled than 
the other, and take them out the same way. In suspending 
the sheets in the bath, care should be had to bring them as 
soon as possible in contact with the conducting rod, a neglect 
of this rule being apt to produce blackish streaks and stains. 

The tanks used for nickeling sheet-zinc are generally about 
7 feet long in the clear, 1^ feet wide, and 2^ to 2J feet deep. 
In such tanks sheets 6 \ feet long and \\ feet wide can be 
conveniently nickeled. 

With the use of a nickel bath according to formula VIII, p. 
258, for nickeling sheet-zinc, the most suitable electro-motive 
force is 3.5 volts and 1 ampere current-density per square deci- 
meter, in order to obtain in three minutes an effective deposit. 
After working for some time this bath also requires a stronger 
•electro-motive force. • 

If zinc is to be nickeled in baths conducting with greater 
difficulty, for instance, in a simple solution of nickel-ammo- 
nium sulphate without the addition of conducting salts, or in 
baths containing boric acid, 1.2 to 1.5 amperes and 7 volts 
must be allowed for 1 square decimeter, if nickeling is to be 
■effected in the above-mentioned space of time. 

For nickeling sheet-zinc, rolled anodes are, as a rule, only 



DEPOSITION OF NICKEL AND COBALT. 305 

'used, except when working with baths containing boric acid. 
The anode surface must at least be equal to that of the zinc 
surface. The distance between the anodes and the sheets 
should be from 3 to 3| inches, and when the current-strength 
is somewhat scant the distance may be reduced to 1\ inches. 
The nickel anodes have to be taken from the bath once daily 
and scoured bright with scratch-brushes and sand. For the 
rest, all the rules given for nickel anodes are valid. 

Baths used for nickeling sheet-zinc soon become alkaline in 
•consequence of the powerful current used, which is shown by 
red litmus-paper turning blue. The alkalinity also manifests 
itself by the bath becoming turbid and the nickeling not turn- 
ing out pure white. The slightly acid reaction required is re- 
stored by citric acid solution. The appearance of the dreaded 
black streaks and stains is due either to the current itself being 
too weak, or to its having been weakened by an extremely 
great resistance of the nickel bath ; also to an insufficient me- 
tallic surface of the anodes, which may be either too small or 
not sufficiently metallic on account of tarnishing ; and finally 
to an excessive alkalinity of the bath, or insufficient contact 
of the hooks with the connecting rods. 

The metallic content of the bath must from time to time be 
strengthened by the addition of nickel salt, and the bath 
filtered at certain intervals. When the conductivity abates, 
it has to be restored by the addition of conducting salts. 

When the sheets have been sufficiently nickeled, they are 
allowed to drain off, then plunged into hot water, and, after 
removing the binding screws, dried by gentle rubbing with 
fine sawdust free from sand and passed through a fine sieve 
to separate pieces of wood. In all manipulations, the un- 
nickeled sides are placed together, while a piece of paper of the 
size and form of the sheets is laid between the nickeled sides. 

The nickeled sheets are finally polished, which is effected 
by placing them upon supports and pressing against the 
revolving bob as previously described, the sheets being, how- 
ever, only moderately moistened with oil, and not too much 
20 



306 ELECTRO-DEPOSITION OF METALS. 

Vienna lime applied to the bob. Polishing is done first in 
one direction and then in another, at a right angle to the first. 
After polishing, the sheets are finally cleansed with a piece of 
soft cloth and impalpable Vienna lime, when they should 
show a pure white lustrous nickeling, free from cracks and 
stains, and bear bending and rebending several times without, 
the deposit of nickel breaking or peeling off. 

Nickeling tin-plate. — For handsome and durable nickeling,, 
iin-plate also requires previous coppering. Deposition is 
effected with a less powerful current than for sheet-zinc. 
Freeing from grease is done in the same manner as above- 
described. 

For preparatory polishing of tin-plate, the use of a polish- 
ing compound free from lime and grease is recommended,, 
since a good polish on tin cannot be obtained with Vienna 
lime and oil. Nickeled tin-plate may be polished with Vienna 
lime and stearine oil. 

It may be here mentioned as a remarkable fact that freshly 
nickeled tin-plate will stand every kind of manipulation, such 
as stamping, edging, pressing, etc., but after having been 
stored for a few months, the layer of nickel frequently peels 
of by these operations. 

Nickeling copper and brass sheets. — The treatment of these- 
sheets differs from that of sheet-zinc in that the rough sheets 
are first brushed with emery and then polished with the bob. 

After treating the sheets with hot caustic lye or lime-paste, 
they are pickled by brushing them over with a solution of 1 
part of potassium cyanide in 20 parts of water. They are then 
thoroughly and rapidly rinsed, and immediately brought into 
the bath. To avoid peeling off, the current-density should 
not exceed 0.4 ampere. 

Nickeling sheet-iron and sheet-steel. — Only the best quality 
of sheet should be used for this purpose. After rolling, the 
sheets are freed from scales by pickling, then passed through 
the fine rolls, and finally again pickled. If the nickeled sheets, 
are not to exhibit a high degree of polish, it suffices to brush 



DEPOSITION OF NICKEL AND COBALT. 307 

them before nickeling with a large, broad fiber brush (p. 204) 
and emery No. 00. But for a high luster, such as is generally 
demanded, the sheets have first to be ground. For fine-grind- 
ing the pickled sheets, broad, massive wood rolls, turned and 
directly glued with emery are used. These wheels are 10 to 12 
inches in diameter, and 2 to 4 or more inches long, according 
to the size of the sheets. For the first grinding, the wheels are 
coated with glue and rolled in emery No. 100 to 120, according 
to the condition of the sheets, while emery No. 00 is applied 
to the wheels used for the fine grinding. The grinding is 
succeeded by brushing, as described on page 205. 

After preparing a sufficiently smooth surface, the sheets are 
at once rubbed with a rag moistened with petroleum, or, if 
preferred, with a rag and pulverized Vienna lime. They are 
then scoured wet in the manner described for sheet-zinc. The 
scouring material must be liberally applied, especially if the 
sheets are to be directly nickeled without previous coppering, 
the latter being, however, quite advisable. After rinsing off 
the lime-paste, the sheets are without loss of time brought into 
the nickel bath. 

For nickeling, a bath free from chlorine should by all means 
be used in order to protect the sheets from rusting. The 
current-density should be 0.4 ampere, with which the sheets 
acquire in £ hour a deposit of sufficient thickness. With the 
use of cold, quick nickeling baths the same thickness of the 
deposit may be obtained in 15 minutes. It is not advisable to 
attempt to obtain a heavy deposit in a shorter time, because it 
would lack density which, by reason of greater protection 
against rust, is the principal requisite for nickeled sheet-iron. 

After nickeling, the sheets are rinsed in clean water, then 
plunged into hot water, and dried by rubbing with warm saw- 
dust. After this operation, it is recommended to thoroughly 
dry the sheets in an oven heated to between 176° to 212° F., 
to expel any moisture from the pores, and then to polish them 
with Vienna lime and oil, or with rouge. 

Nickeling wire. Nickeling of wire of iron, brass or copper 



308 ELECTRO-DEPOSITION OF METALS. 

is scarcely ever done on a large scale. It is, however, believed 
that the nickeling of iron and steel wires — for instance, piano- 
strings — might be of advantage to prevent rust, or at least to 
retard the commencement of oxidation as long as possible. 

To nickel single wires cut into determined lengths, accord- 
ing to the general rules already given, is simple enough ; but 
this method cannot be pursued with wire several hundred 
yards long, rolled in coils, as it occurs in commerce. Nickel- 
ing the wire in coils, however, cannot be done, as only the 
upper windings exposed to the anodes would acquire a coat 
of nickel. Hence it becomes necessary to unwind the coil, and 
for continuous working pass the wire at a slow rate through 
the cleansing and pickling baths, as well as the nickel bath, 
and hot water reservoir, as shown in Fig. 119, in cross-section, 
and in Fig. 120, in ground plan. 

The unwinding of the wire is effected by a slowly revolving 
shaft, upon which the nickeled wire again coils itself; but in 
the illustration the shaft is omitted. In Fig. 120 four wires run 
over the four rolls a, mounted upon a common shaft, to the 
rolls b upon the bottom of the tank A, whereby they come in 
•contact with a thickly-fluid lime-paste in the vat, and are freed 
from grease. From the rolls 6 the wires run through the 
wooden cheeks i, lined with felt, which retain the excess of 
lime-paste, and allow it to fall back into the tank. The wires 
then pass over the roll c to the roll d. Between these two rolls 
is the rose g, which throws a powerful jet of water upon the 
wires, thereby freeing them from adhering lime-paste. The 
roll d, as well as its axis, is of brass, and to the latter is con- 
nected the negative pole of the battery or dynamo, so that by 
carrying the wires over the roll d, negative electricity is con- 
ducted to them. From the roll d, the wires run over the roll- 
bench s (Fig. 119) to the tank C, which contains the nickel 
solution, so that they are subjected to the action of the anodes 
arranged in this tank on both sides of the wires. The wires 
then pass over the roll e, are rinsed under the rose h, and run 
finally through a hot-water reservoir and sawdust (these two 



DEPOSITION OF NICKEL AND COBALT. 



309 



apparatuses are not shown in the illustration), to be again 
wound in coils. In case a high polish is required, the nick- 







v5* 



# 






H 



>/^V. CO' 

tew , 

V,*. / 



■ I \Vs\ 



rnun 



4w- 



sill 



yifif u 



eled wires may be run under pressure through leather cheeks 
dusted with Vienna lime. 



310 ELECTRO-DEPOSITION OF METALS. 

Nickeling knife-blades, sharp surgical instruments, etc. Con- 
siderable trouble is frequently experienced in nickeling sharp- 
■edged instruments, the edges and points being spoiled either 
by the deposit of nickel or in polishing. And yet such instru- 
ments can be readily nickeled in such a manner that the 
edges remain in as good condition as before. 

If new instruments which have never been used are to be 
nickeled, no special preparation is required, it being only nec- 
essary to free them at once from grease and bring them into 
the bath. But instruments which have been used or, by bad 
treatment have become partly or entirely covered with rust, 
must be first freed from rust by chemical or mechanical treat- 
ment, and then polished. The marks left by the stone or 
emery wheel are effaced by means of the circular brush, this 
treatment being necessary to obtain perfect nickeling. But, 
in brushing, the edges are rendered dull if special precaution- 
ary measures are not used. For instance, the edge of a knife- 
blade must never come in contact with the brush. This is 
prevented by firmly pressing the blade flat upon a soft sup- 
port of felt or cloth, so that the edge sinks somewhat into the 
support, without, however, cutting into it. The edge is then 
held downward, and thus together with the support brought 
against the revolving brush. In this manner the blades may 
be vigorously brushed without fear of spoiling the edges. 

The treatment for giving them a high polish after nickeling 
is the same. Freeing from grease may be done in the usual 
manner with lime-paste ; but must also be effected upon a soft 
support, the same as in polishing. After thorough rinsing in 
clean water, the separate pieces, without being previously cop- 
pered, are brought directly into the nickel bath, the composi- 
tion of which must, of course, be suitable for nickeling steel 
articles. The instruments are first coated with the use of a 
strong current, so that deposition takes place slowly and with 
great uniformity. 

In suspending the articles in the bath, care should be had 
that neither a point nor an edge is turned towards the anodes. 



DEPOSITION OF NICKEL AND COBALT. 311 

It is best to use a bath with anodes on one side only, and to 
suspend the blades with their backs towards the anodes. If, 
for any reason, the instruments are to be suspended between 
two rows of anodes, the edges should be uppermost, as near as 
possible to the level of the bath ; but they should never hang 
deep or downwards. 

These precautionary measures may be omitted by using for 
nickeling such articles with sharp edges, the bath consisting of 
nickel sulphate and sodium citrate, which has been previously 
mentioned. In this bath, the edges and points of the instru- 
ments do not burn as readily as in oiher nickel baths, and the 
deposited nickel being soft, it does not show a tendency to 
peeling off when, after nickeling, the edges of the instruments 
are sharpened. 

The plated instruments are given a finer luster by polishing, 
but during this operation they must always be exposed upon 
a soft support, as above described, to the action of a felt wheel, 
or, still better, of a cloth bob. 

In nickeling skates it is advisable to suspend them so that 
the runners hang upwards and that the running surfaces are 
level with the surface of the bath, because if the deposit upon 
the running surfaces is too thick, it peels off readily when 
injured by grains of sand upon the ice. 

Nickeling of soft alloys of lead and tin, with or without addi- 
tion of antimony, as are used for siphon-heads, etc., is effected, 
in case the objects have already a high luster, by freeing them 
from grease with whiting and a small quantity of Vienna lime, 
then rinsing in water, lightly coppering, or better, brassing, 
and finally nickeling in a bath containing chlorine. 

If the objects require preparatory polishing, use a polishing 
"compound free from lime and grease, as given under nickeling 
of tin-plate, rinse with benzine, immerse in hot water, and free 
from grease with whiting and Vienna lime. Then brass, 
nickel and polish. Direct nickeling without previous brass- 
ing is not advisable, waste in consequence of peeling off being 
frequently the result. 



312 ELECTRO-DEPOSITION OF METALS. 

Nickeling printing plates {stereotypes, cliches, etc.). The ad- 
vantages of nickeling stereotypes, etc., over steeling will be 
referred to under " Steeling," and hence only the most suit- 
able composition of the nickel baths and the manipulation 
required will here be given. 

The nickel baths according to formula I (page 253) and 
formula VII (page 257) are the most suitable for simple 
nickeling, because the ammonium sulphate not being present 
in too great an excess, as well as the presence of boric acid,. 
causes the nickel to separate with considerable hardness. 
With nickeled stereotypes three times as large an edition 
can be printed as with plates of the same material not 
nickeled. 

Hard nickeling. It being a well-known fact that a fused 
alloy of nickel with cobalt possesses greater hardness than 
either of the metals by themselves, experiments proved that 
an electro-deposited nickel-cobalt alloy exhibited the same be- 
havior, the greatest degree of hardness being attained with an 
addition of cobalt varying between 25 and 30 per cent. For 
this deposit the term hard nickeling is proposed, the most suit- 
able bath for the purpose being prepared according to the 
following formula : 

Nickel-ammonium sulphate 21.16 ozs., cobalt-ammonium 
sulphate 5.29 ozs., crystallized boric acid 8.8 ozs., water 10 to 
12 quarts. 

To prepare the bath dissolve the constituents by boiling 
as given under formula VII, p. 257. In case the metal salts 
should contain free acids add, previous to the addition of the 
boric acid, a small quantity of nickel carbonate. The boric 
acid must not be neutralized and the bath should work with 
its acid reaction. Mixed anodes in the proportion of ^ cast 
and § rolled, are to be suspended in the bath. 

The bath prepared according to formula No. II deserves the 
preference, it yielding a harder deposit than bath No. I. 

For the rest, the treatment of the baths is the same as that 
given for nickel baths of similar composition (pp. 253 and. 



DEPOSITION OF NICKEL AND COBALT. 



313 



257), and the process of hard nickeling does not essentially 
differ from ordinary nickeling. The suspending hooks are 
soldered to the backs of the plates by means of the soldering- 
iron and a drop of tin ; or the plates are secured in holders 
of sheet-copper 0.11 inch thick, and £ to 1 inch wide, of the 
form shown in Fig. 121. The printing surface is freed from 
grease by brushing with lime-paste, rinsing in water, and then 
brushing with a clean brush to remove the lime from the 
depressions. The plates are then hung in the bath and. 

Fig. 121. 




covered with a strong current. When everywhere coated' 
with nickel, the current is weakened and the deposit allowed 
gradually to augment. With an average duration of nickel- 
ing of 15 to 20 minutes, with 2.8 to 3 volts, the deposit will, 
as a rule, be sufficiently resisting. 

Stereotypes of type metal, after being freed from grease, are 
best lightly coppered in the acid copper bath, then rinsed and 
brought into the nickel bath. Zinc etchings are first coppered, 
not too slightly, in the copper cyanide bath,, rinsed, and sus- 



-314 ELECTRO-DEPOSITION OF METALS. 

pended in the nickel bath with a very strong current. With 
too weak a current, black streaks are formed, zinc is dissolved, 

-and both the plate and bath are spoiled. With copper elec- 
tros, pickling with potassium cyanide solution, after freeing 

.from grease, must not be omitted. 

The nickeled plates are rinsed in water, then plunged in 
hot water, and dried in sawdust, when the nickeled printing 
surface may be brushed over with a brush and fine whiting, it 
being claimed that plates thus treated take printing ink better, 
while the first impressions of plates not brushed with whiting 
are somewhat dull. 

Nickel-facing is especially suitable for copper plates for 

•color-printing, the nickel not being attacked like copper or 
iron by cinnabar. 

Recovery of nickel from old baths. At the present price of 
nickel its recovery from old solutions scarcely pays. The ineffi- 
ciency of the bath is in most cases due to two causes : It has 
either become too poor in metal or it contains foreign metallic 
admixtures. In the first case, the expense of evaporating, to- 
gether with the further manipulations, is out of proportion to 
the value of the nickel recovered, and, in the second case, the 
reduction of the foreign metals is inconvenient and connected 
with expense which make it unprofitable. The recovery of 
nickel from old baths which have become useless, by the elec- 
tric current with the use of carbon-plate anodes, as here and 
there recommended, is the most disastrous and expensive of 
all, and can only be condemned. 

For nickeling by contact and boiling, see special chapter, 
'" Depositions by Contact." 

Deposition of nickel alloys. — From suitable solutions of the 
metallic salts nickel may be deposited together with copper 
and tin, as well as with copper and zinc. With the first 
combination, especially, all tones from copper-red to gold- 
shade may be obtained, according to which metal predomi- 
nates, or according to the current-strength which is conducted 
into the bath, as is also the case in brassing. 



DEPOSITION OF NICKEL AND COBALT. 315 

A suitable bath for coating metallic articles with an alloy 
•of nickel, copper and tin, for which the term nickel-bronze is 
proposed, is obtained by dissolving the metallic phosphates in 
sodium pyrophosphate solution. By mixing solution of blue 
vitriol with solution of sodium phosphate, cupric phosphate is 
precipitated, which is filtered off and washed. In the same 
manner nickel phosphate is prepared from a solution of nickel 
sulphate. These phosphates are then, each by itself, dis- 
solved in a concentrated solution of sodium pyrophosphate, 
while chloride of tin is directly dissolved in sodium pyro- 
phosphate until the turbidity, at first rapidly disappearing, 
disappears but slowly. 

Nothing definite can be said in regard to the mixing pro- 
portions of these three solutions, because the proportions will 
have to be varied according to the desired color of the de- 
posit. The operator, however, will soon find out, of which 
solution more has to be added to obtain the tone desired. 

For depositing a nickel-copper-zinc alloy solutions of cupric 
sulphate (blue vitriol) and zinc oxide in potassium cyanide 
to which is added an ammoniacal solution of nickel carbonate, 
may be advantageously used. As will be seen a deposit of 
'German silver can be obtained with the use of this solution if 
the latter contains the metals in the same proportions as 
•German silver, and German silver anodes are used. 

According to a French process, a deposit of German silver 
may be obtained as follows : Dissolve a good quality of Ger- 
man silver in nitric acid and add, with constant stirring, 
solution of potassium cyanide until all the metal is precipitated 
as cyanide. The precipitate is then filtered off, washed, dis- 
solved in potassium cyanide, and the solution diluted with 
double the volume of water. This process, however, does not 
seem very feasible, since nickel separates with difficulty from 
its cyanide combination. 



316 electro-deposition of metals. 

Examination of Nickel Baths. 

The reaction of the nickel baths have previously been 
briefly referred to, but the subject must here be more closely 
considered. 

For -the determination of the content of acid, a different 
method must be adopted according to the composition of the 
bath, i. e., whether it has been prepared with an addition of 
citric acid, boric acid, etc. The reddening of blue litmus- 
paper simply indicates the presence of free acid in the bath, 
but leaves. us in the dark as to which acid is present, and as 
to its derivation. 

If, for instance, in consequence of insufficient solution of 
nickel, free sulphuric acid appears on the anodes, the bath be- 
comes at the same time poorer in nickel in proportion to the 
increase in the content of free sulphuric acid. If we have to' 
deal with a bath prepared from nickel-ammonium sulphate with 
an addition of ammonium sulphate, but without organic acids, 
the reddening of blue litmus-paper will at once indicate a con- 
tent of free sulphuric acid, if the bath was neutral in the begin- 
ning. It is, however, quite a different matter when a bath con- 
taining boric acid is examined. In the formula? for preparing 
these baths, it has been seen that before adding the boric acid, 
any free sulphuric acid of the nickel salt present is to be re- 
moved by treating the solution with nickel carbonate or nickel 
hydrate. After adding the boric acid, blue litmus-paper is 
strongly reddened, and this acidity due to the boric acid is to 
be maintained in the bath. However, in consequence of the 
use of too large a number of cast anodes, free sulphuric acid 
may form in the bath, and this, together with boric acid, can- 
not be recognized by blue litmus-paper, since both acids red- 
den it. In this case red congo paper, which is not changed 
by boric acid, but is turned blue by sulphuric acid, has to be 
used. If red congo paper is colored blue, it is a sure proof 
that, besides boric acid, free sulphuric acid is present, which 
has to be neutralized for the bath to work in a correct 
manner. 



DEPOSITION OF NICKEL AND COBALT. 317 

The process is again different when a bath prepared with 
an addition of citric acid is to be examined. This organic 
acid colors certain varieties of commercial congo paper blue, 
just as sulphuric acid does, and hence tropaeolin paper has to 
be used, which is not altered by citric acid, but is colored 
violet by free sulphuric acid. 

If a nickel bath has been prepared with the addition of 
organic salts, for instance, sodium citrate, ammonium tartrate 
or others, the formation of free sulphuric acid in the bath 
cannot at first be determined with reagent papers, because the 
sulphuric acid decomposes the organic salts, neutral sulphates 
being formed, and a quantity of organic acid equivalent to 
the sulphuric acid is liberated. For this reason the content 
of metal in the bath declines, though the presence of sulphuric 
acid cannot be established, because the sulphuric acid formed 
by electrolysis is not consumed for the solution of nickel on 
the anodes, but for the decomposition of the organic salts. 

Now let us suppose the reverse, namely, that in a nickel 
bath prepared with the addition of one of the above-mentioned 
acids, free ammonia appears in consequence of the sole use of 
cast anodes, and of the decomposition of ammonium sulphate 
by a strong current. This phenomenon cannot at once be 
recognized, because the ammonia is first fixed by the free 
acid, and the bath becomes neutral or alkaline only when all 
the free acid which was present has been consumed for fixing 
the ammonia formed. With this process there will generally 
be connected an increase in the content of the metal, and it 
will be seen, without further explanation, that for the accurate 
determination of the processes and alterations in a nickel bath 
when in operation, the quantitative determination of the free 
acids, and as much as possible, that of the content of metal, is 
required. 

Although it may be said that the busy electro-plater will 
frequently not feel inclined to familiarize himself with the 
methods of testing, and seldom have the necessary time for 
executing the determinations of the content of metal, neverthe- 



318 ELECTRO-DEPOSITION OF METALS. 

less the methods will here be described with sufficient detail,, 
so that those who wish to examine their baths in this respect 
will find the necessary instructions. To be sure, if the electro- 
plater himself is not a practical analytical chemist he will have 
to be taught by some one thoroughly conversant with the sub- 
ject the management of the analytical balance, how to execute 
the weighings, etc. It is also advisable to procure the stand- 
ard solutions required for volumetric analysis from a reliable 
chemical laboratory, in order to avoid the possibility of arriv- 
ing at incorrect results by the use of inaccurately prepared 
standard solutions. For this reason directions for the prepa- 
ration of standard solutions are omitted, and the methods of 
examination in use for our purposes will now be given. 

The examinations may be made by gravimetric analysis- 
analysis by weight), volumetric analysis (analysis by meas- 
ure), and by electrolytic analysis. The first method is based 
chiefly upon the precipitation in an insoluble form of the con- 
stituent to be determined, and filtering, washing, drying, and 
weighing the precipitate. This method requires considerable- 
knowledge of chemistry and analytical skill, and should only 
be resorted to by those not versed in analysis when other 
more practical methods for the determination of the contents-, 
such as volumetric and electrolytic methods, are not known. 

Volumetric analysis is based upon a very different principle 
from that of gravimetric analysis. The constituent to be ascer- 
tained is quantitatively determined by means of a standard 
solution, enough of which is used until the final reaction shows 
that a sufficient quantity has been added. From the known 
content of the standard solution the constituent to be deter- 
mined is then calculated. This may be explained by an 
example. For instance, the content of sulphuric acid in a 
fluid is to be determined. Measure the quantity of fluid by 
means of a pipette which up to a mark holds exactly 10 cubic 
centimeters. Allow the fluid to run into a clean beaker, 
dilute with about 30 cubic centimeters of water, and heat to 
about 122° F. Now, while constantly stirring the fluid in 



DEPOSITION OF NICKEL AND COBALT. 319' 

the beaker with a glass rod, add standard soda solution from, 
a glass burette provided with a glass cork and divided into-n,- 
cubic centimeters until a piece of congo paper when touched 
with the glass rod is no longer colored blue. The addition of 
the standard soda solution must, of course, be effected with 
great care. So long as the congo paper shows a vivid blue 
color, a larger quantity may at one time be added, but when 
the colorization becomes less vivid, the solution is added drop 
by drop so as to be sure that the last drop is just sufficient to 
prevent the blue coloration which was still perceptible after 
the addition of the previous drop. The drop-test must, of 
course, be made upon a dry portion of the congo paper, which 
has not been previously moistened. When no blue coloration 
appears after the last drop has been added, it is a proof that 
all the sulphuric acid present has been neutralized by the 
standard soda solution. The number and fractions of cubic 
centimeters consumed are then read off on the burette, and 
the quantity of sulphuric acid present is calculated as fol- 
lows : 1 cubic centimeter of standard soda solution neutralizes 
0.049 gramme of sulphuric acid (H 2 S0 4 ), and hence the- 
quantity of sulphuric acid is obtained by multiplying the 
number of cubic centimeters of standard soda solution by 
0.049. Now, since 10 cubic centimeters were measured off 
by the pipette and titrated, the number found is multiplied 
by 100, which gives the content of sulphuric acid in 1 liter of' 
the fluid. 

If, for instance, for the neutralization of 10 cubic centi- 
meters of the fluid containing sulphuric acid, 5.4 cubic centi- 
meters of standard soda solution were required, then the 
content of sulphuric acid amounts to 5.4x0.049=0.2646 
gramme, or in 1 liter to 0.2646 X 100 = 26.46 grammes. 

The electrolytic method of analysis is available only for the- 
determination of such metals as can be completely separated 
in a coherent form from their solutions by the current. It is- 
based upon the fact that the metallic solution contained in a* 
platinum dish is decomposed by the current, and the metah 



320 



ELECTRO-DEPOSITION OF METALS. 



precipitated upon the platinum dish. After washing and 
drying, the dish is weighed and the weight of the precipitated 
metal is obtained by deducting the weight of the platinum 
dish without precipitate, which, of course, has been ascertained 
before making the experiment. 

The apparatus generally used for electrolytic analysis is 
shown in Fig. 122. The platinum dish, holding about |- liter, 
rests upon a metal ring which is secured to the rod of the 
stand, and is in contact with the negative pole of the source 

Fig. 122. 




of current. Into the dish, at a distance of 1 or 2 centimeters 
from the bottom, dips a round platinum disk bent like the 
bottom, or a spiral of platinum wire, 1 millimeter thick, which 
serves as an anode and is secured by platinum wire in a mov- 
able support or holder. The latter is carefully insulated from 
the rod of the stand and connected with the positive pole of 
the source of current. During electrolysis the platinum dish 
is covered with a perforated watch-glass to prevent possible 
•loss by the evolution of gas. 



DEPOSITION OF NICKEL AND COBALT. 321 

Since many precipitates have to be washed without inter- 
rupting the current, it is best to use the washing contrivance 
shown in the illustration to prevent the precipitated metal 
from being redissolved by the electrolyte. With the upper 
clip closed, the shorter leg of the siphon is dipped into the 
dish. The lower clip is then closed and the upper one opened 
until the short leg is filled with water. The upper clip is 
then closed and the lower one opened, whereby the dish is 
emptied. The clip of the longer leg of the siphon is then 
•closed, the uppermost clip opened, and the dish filled up to 
the rim with water. The uppermost clip is then closed, the 
lower one opened, and the dish emptied the second time, the 
operation being repeated until the precipitate and dish are 
thoroughly washed. 

Since for complete electrolytic precipitation it is essential to 
operate with correct electro-motive forces, it is advisable to 
use an accurate ammeter adjusted to 0.05 to 2.5 amperes, as 
well as a voltmeter. 

The current for electrolysis may be supplied by cells, a 
thermo-electric pile, a dynamo, or an accumulator, but the 
necessary regulating resistances must in every case be provided. 

Let us now return to the examination of nickel baths. If 
by qualitative analysis the presence of free sulphuric acid in 
the bath has been established, it can be at once assumed that 
the content of nickel has from the first declined. Hence it 
will scarcely be worth while to determine by volumetric analy- 
sis the quantity of free sulphuric acid present, and to calculate 
from this the quantity of nickel carbonate or nickel hydrate 
required for neutralization. It will be only necessary to add 
to the bath, stirring constantly, small portions of the nickel 
salt rubbed up with water, until a fresh test with congo paper 
shows no blue coloration. The addition of a small excess of 
nickel carbonate or nickel hydrate is unobjectionable. Besides 
neutralizing the free sulphuric acid, care should at the same 
time be taken to prevent its further formation by increasing 
the number of cast-nickel anodes. The case is similar when 
22 



322 ELECTRO-DEPOSITION OF METALS. 

a nickel bath prepared with organic salts, for instance, with 
potassium citrate or sodium citrate, is to be examined. Even 
if it is shown by the reaction that no free sulphuric acid is 
present, the content of nickel, as previously mentioned, may 
have decreased, and the content of free organic acid increased. 
The latter may, however, be neutralized by the addition of 
nickel carbonate or nickel hydrate, and hence the determina- 
tion of the content of acid by volumetric analysis is not. 
absolutely necessary. 

When, on the other hand, a nickel bath has become alkaline,, 
the determination of the free alkali by volumetric analysis will 
be of little value, and it will, according to the composition of 
the bath, suffice to neutralize it with dilute sulphuric acid, or 
acidulate it with an organic acid. Since, however, baths which 
have become alkaline possess a higher content of nickel than 
the normal bath, an electrolytic determination of the nickel 
may be of use in order to calculate accurately the quantity of 
water which has to be added to reduce the content of nickel 
to the normal quantity. 

If the bath has been prepared with nickel-ammonium sul- 
phate with additions of ammonium sulphate, or boric acid, or 
if it contains only very small quantities of organic acids, it 
can be directly electrolyzed. 

Bring by means of the pipette exactly 20 cubic centimeters- 
of the bath into the platinum dish, add 4 grammes of ammo- 
nium sulphate and 35 to 40 cubic centimeters of ammonia of 
0.96 specific gravity and electrolyze with a current-density = 
0.6 ampere until no dark coloration appears after adding a 
drop of ammonium sulphate to a few cubic centimeters of the- 
electrolyte. Rinse the dish, together with the precipitate, with 
water, remove the water by rinsing with absolute alcohol, rinse- 
the dish with pure ether and dry at 212° F. in an air-bath. 
The weight of the precipitate of metallic nickel obtained by 
weighing the platinum dish gives the content of nickel am- 
monium sulphate in grammes per liter of bath b} 7- multiplying 
by 335. From the increase in the content of nickel ammo- 



DEPOSITION OF NICKEL AND COBALT. 323 

ilium sulphate shown by the analysis, it can be readily cal- 
culated how much water has to be added to the bath to reduce 
it to the original content. 

If a nickel bath contains large quantities of organic acids, 
precipitate 20 cubic centimeters of the bath with sodium sul- 
phide solution, filter and wash the precipitate, dissolve it in 
nitric acid, and evaporate the solution with pure sulphuric 
acid upon the water-bath to drive off the nitric acid. The 
residue is treated as above described. 

2. Deposition of Cobalt. 

Properties of cobalt. Cobalt (Co = 58.97 parts by weight) 
has nearly the same color as nickel, with a slightly reddish 
tinge ; its specific gravity is 8.7. It is exceedingly hard, 
highly malleable and ductile, and capable of taking a polish. 
It is slightly magnetic, and preserves this property even when 
alloyed with mercury. It is rapidly dissolved by nitric acid, 
and slowly by dilute sulphuric and hydrochloric acids. 

For plating w r ith cobalt, the baths given under " Nickeling " 
may be used by substituting for the nickel salt a correspond- 
ing quantity of cobalt salt. By observing the rules given 
for nickeling, the operation proceeds with ease. Anodes of 
metallic cobalt are to be used in place of nickel anodes. 

Nickel being cheaper and its color somewhat whiter, electro- 
plating with cobalt is but little practiced. On account of the 
greater solubility of cobalt in dilute sulphuric acid, it is, how- 
ever, under all circumstances, to be preferred for facing valu- 
able copper plates for printing. 

According to the more or less careful adjustment of such 
plates in the press, the facing in some places is more or less 
attacked, and it may be desired to remove the coating and 
make a fresh deposit. For this purpose Gaiffe has proposed 
the use of cobalt in place of nickel, because the former dis- 
solves slowly but completely in dilute sulphuric acid. He 
recommends a solution of 1 part of chloride of cobalt in 10 of 
water. The solution is to be neutralized with aqua ammonia, 



324 ELECTRO-DEPOSITION OF METALS. 

and the plates are to be electro-plated with the use of a 
moderate current. 

Cobalt precipitated from its chloride solution, however, does 
not yield a hard coating, and hence the following bath is 
recommended for the purpose: Double sulphate of cobalt and 
ammonium 21 ozs., crystallized boric acid 10J ozs., water 10 
quarts. 

The bath is prepared in the same manner as No. VII, given 
under " Deposition of Nickel." It requires an electro-motive 
force of 2.5 to 2.75 volts ; current-density, 0.4 ampere. 

Prof. Sylvanus Thompson's solutions for the electro-deposi- 
tion of cobalt, patented by him in 1887, yield very satisfactory 
results : 

I. Double sulphate of cobalt and ammonium 16 ozs., mag- 
nesium sulphate 8 ozs., ammonium sulphate 8 ozs., citric acid 
1 oz., water 1^ gallons. 

II. Cobalt sulphate 8 ozs., magnesium sulphate 4 ozs., 
ammonium sulphate 4 ozs., water 1^ gallons. It is best to 
use the solutions warm, at about 95° F. 

To determine whether copper, and how much of it, is dis- 
solved in stripping the cobalt deposit from cobalted copper 
plates, a copper plate with a surface of 7| square inches was 
coated with 7.71 grains of cobalt and placed in dilute sul- 
phuric acid (1 part acid of 66° Be. to 12.5 parts of water). 
After the acid had acted for 14 hours, the cobalt deposit was 
partially dissolved, and had partially collected in laminae 
upon the bottom of the vessel, the copper plate being entirely 
freed. On weighing the copper plate it was shown that it 
had lost about 0.0063 per cent., this loss being apparently 
chiefly from the back of the plate, the engraved side exhibit- 
ing no trace of corrosion. The experiment proved that there 
is no danger of destroying the copper plate b} r stripping the 
cobalt deposit with dilute sulphuric acid, provided the opera- 
tion is executed with due care and attention. 

Warren has described a cobalt solution which can be decom- 
posed in a single-cell apparatus, and for this reason would seem 



DEPOSITION OF NICKEL AND COBALT. 325 

suitable for electro-plating small articles in quantities. For 
the preparation of this bath, dissolve 3J ounces of chloride of 
cobalt in as little water as possible, and compound the solution 
with concentrated solution of Rochelle salt until the volumi- 
nous precipitate at first formed is almost entirely redissolved, 
and then filter. Bring the bath into a vessel and place the 
latter in a clay cup filled with concentrated solution of chlo- 
ride of ammonium or of common salt, and containing a zinc 
cylinder. Connect the objects to be plated to the zinc by a 
copper wire, and allow them to dip in the cobalt solution. 
With a closed circuit the objects become gradually coated 
with a lustrous cobalt deposit which, after 2 hours, is suffi- 
ciently heavy to bear vigorous polishing with the bob. Coat- 
ing zinc in the same manner was not successful. 



CHAPTER VII. 

DEPOSITION OF COPPER, BRASS AND BRONZE. 
1. Deposition of Copper. 

Properties of copper. Copper (Cu = 63.57 parts by weight) 
lias a characteristic red color, and possesses strong luster. It 
is very tenacious, may be rolled to thin laminae, and readily 
drawn into fine wire. The specific gravity of wrought copper 
is 8.95, and of cast, 8.92. Copper fuses more readily than 
gold, but with greater difficulty than silver. 

In a humid atmosphere containing carbonic acid, copper 
becomes gradually coated with a green deposit of basic car- 
bonate. When slightly heated it acquires a red coating of 
cuprous oxide, and when strongly heated a black coating of 
cupric oxide with some cuprous oxide. Copper is most read- 
ily attacked by nitric acid, but is slowly dissolved when im- 
mersed in heated hydrochloric or sulphuric acid. With 
exclusion of the air, it is not dissolved by dilute sulphuric or 
hydrochloric acid," and but slightly with admission of the air. 
Liquid ammonia causes a rapid oxidation of copper in the 
air and the formation of a blue solution. An excess of potas- 
sium cyanide dissolves copper. Sulphuretted hydrogen black- 
ens bright copper. 

Copper baths. The composition of these baths depends on 
the purpose they are to serve, and below are mentioned the 
most approved baths, with the exception of the acid copper 
bath used for plastic deposits of copper, which will be dis- 
cussed later on under " Copper Galvanoplasty." 

In most cases the more electro-positive metals, zinc, iron, 
tin, etc., are to be coppered either as preparation for the suc- 
ceeding processes of nickeling, silvering, or gilding, or to pro- 

(326) 



DEPOSITION OF COPPER, BRASS AND BRONZE. 327 

<tect them against oxidation, or for the purpose of decoration. 
The above-mentioned electro-positive metals, however, decom- 
pose acid copper solutions and separate from them pulverulent 
•copper, while an equivalent portion of zinc, iron, tin, etc., is 
dissolved. For this reason, such solutions cannot be used for 
coating these metals, and alkaline copper baths are exclusively 
employed, which may be arranged under two groups — those 
containing potassium cyanide, and those without it. 

Copper cyanide baths are prepared by dissolving cupric salts, 
for instance, cupric acetate (verdigris), cupric sulphate (blue 
vitriol), or cuprous compounds, such as cuprous oxide, in 
potassium cyanide, the salts being thereby converted into 
potassium-copper cyanide, which is the effective constituent 
of all copper cyanide baths. 

By compounding a solution of a cupric salt with potassium 
cyanide, cupric cyanide is formed, which is very unstable, 
rapidly changing by exposure into cupro-cupric cyanide and 
-cyanogen gas. To avoid this loss of cyanogen, sulphites are 
added, which, according to one view, effect a reduction of the 
-cupric salts to cuprous salts, which dissolve in potassium 
cyanide without cyanogen being liberated, while, according 
1;o another, hydrocyanic acid is produced from cyanogen gas 
^,nd sodium sulphite, water being decomposed, and forms 
with the sodium carbonate present, sodium cyanide, the latter 
becoming again active in converting the cupro-cupric cyanide 
into the soluble double salt. It is possible that both the 
reactions mentioned above partly appear together. 

By using from the start cuprous oxide, the latter can with- 
out loss of cyanogen be converted into potassium-copper 
cyanide. 

In accordance with this, there will be given in the formulas 
for the preparation of potassium-copper cyanide baths in 
which cupric salts are used, larger or smaller additions of 
bisulphite of soda and alkaline carbonates, the former serving 
the purpose of decreasing the loss of cyanogen, and the latter 
•being intended to fix any free acid formed. 



328 ELECTRO-DEPOSITION OF METALS. 

Stockmeier was the first to take the trouble of calculating 
the combinations formed after the conversion of the separate 
constituents of the copper baths, and Jordis has adopted the 
same course, in order to obtain a standard formula. Both 
these authors recommend not to produce the copper combina- 
tion actually subjected to electrolysis in the bath by repeated 
conversions of salts, but to prepare this combination by itself, 
and to dissolve it direct in water in order to obtain the finished 
copper bath. It has been shown in practice that this method 
is quite practicable provided certain points are taken into con- 
sideration. However, the rational composition of a bath with 
potassium cyanide, which has been produced by conversion 
from the salts, cannot be judged according to whether the sep- 
arate salts were present in stoichoimetrical proportions for the 
smooth conversion into new combinations without receiving in 
the bath an excess from one or the other substance. In prac- 
tice it has long been known that an excess of sodium bisulphite 
has a very beneficial effect upon the separation of a lustrous 
copper, and prevents it from rapidly turning into a dull earthy 
gray, this effect being very likely due to the prussic acid lib- 
erated by the sulphurous acid. This one example may prove 
that standard formulas erected upon theoretical maxims should 
be accepted with due caution by the practical electro-plater,, 
and that, under certain conditions, additions will have to be 
made to baths prepared according to such standard formulas 
if the result is to be as good as that from baths prepared 
according to older formulas. 

Hossauer prepares a copper bath by dissolving 3J ozs. of" 
copper cyanide in a solution of 17J ozs. of 70 per cent, potas- 
sium cyanide in 3 quarts of water, boiling, filtering and dilu- 
ting with 7 quarts of water, to a 10-quart bath. This bath 
works very well when heated to between 113° and 122° F., 
but when used cold requires a very strong current. 

Roseleur has recommended the use of copper acetate (ver- 
digris) for copper baths, and suitable compositions, slightly 
modified, are as follows : 



DEPOSITION OF COPPER, BRASS AND BRONZE. 829 

Copper baths for iron and steel articles. — I. To be used at the 
ordinary temperature. Water 10 quarts, bisulphite of soda in 
powder 7 ozs., crystallized carbonate of soda 14 ozs., neutral 
copper acetate 7 ozs., 75-per cent, potassium cyanide 7 ozs., 
ammonia 4.4 ozs. 

II. For hot coppering (at between 14-0° and 158° F.). Water 
10 quarts, bisulphite of soda in powder 2£ ozs., crystallized 
carbonate of soda 7 ozs., neutral copper acetate 7 ozs., 75. per 
cent, cyanide of potassium 6f ozs., ammonia 4 ozs. 

The baths are best prepared as follows : Dissolve the bisul- 
phite and carbonate of soda in one-half of the water, the potas- 
sium cyanide in the other half, and mix the copper salt with 
the ammonia ; then pour the blue ammoniacal copper solution 
into the solution of the soda salts, and finally add the potas- 
sium cyanide solution ; the bath will then be clear and color- 
less. Boiling, though not absolutely necessary, is of advan- 
tage, after which the solution is to be filtered. 

According to thorough investigations made, the excess of 
carbonate of soda in formula I serves no special purpose, but 
on the contrary, in many cases, is directly detrimental ; 
neither is the use of ammonia of any special advantage, and 
it may just as well, or rather -better, be omitted. Further, 
the use of separate baths for cold and warm coppering is at 
least questionable. It is believed that a single bath suffices 
for both cases, heating having been found of special advantage 
only for rapid and thick coppering, or for obtaining particu- 
lar shades which are produced with difficulty in the cold, 
bath, but without trouble in the heated bath. 

It should be borne in mind that potassium cyanide solu- 
tions are still more rapidly decomposed when heated than 
when used cold, and consequently the consumption of potas- 
sium cyanide in heated baths is considerably greater than in 
cold baths. Recourse to heating should, therefore, only be 
had when the intended result cannot by any other means be 
obtained. 

The following formula may be highly recommended, a 



; 330 ELECTRO-DEPOSITION OF METALS. 

copper bath composed according to it always yielding good 
and sure results. 

III. Water 10 quarts, crystallized carbonate of soda 8 \ ozs., 
crystallized bisulphite of soda 7 ozs., neutral copper acetate 
7 ozs., 98 or 99 per cent, potassium cyanide 8^- ozs. 

Electro-motive force at 10 cm. electrode-distance, 3 volts. 

Current-density, 0.35 ampere. 

The bath is prepared as follows : Dissolve in 7 quarts of 
warm water the carbonate of soda, gradually add the bisul- 
phite of soda to prevent violent effervescence, and then add, 
with vigorous stirring, the copper acetate in small portions. 
Dissolve the potassium cyanide in 3 quarts of cold water, and 
mix both solutions when the first is cold. By thorough stir- 
ring with a clean wooden stick, a clear solution is quickly 
obtained, which is allowed to settle and siphoned off clear. 
If after the addition of the potassium cyanide the bath should 
not become colorless, or at least wine-yellow, add a small 
quantity more of potassium cyanide. 

When conversion is complete, the bath contains potassium- 
copper cyanide, potassium acetate, sodium acetate, sodium 
sulphate, and potassium cyanide in excess in addition to 
sodium bisulphite. 

For certain purposes, for instance, for the production of a 
very close, thick deposit, as required for cast-iron door knobs, 
etc., it is advisable to double the content of metal. For the 
preparation of such a copper bath it is only necessary to dis- 
solve double the quantities of the salts given in formula III 
in 10 quarts of water. 

Stockmeier recommends the following copper bath: 

Ilia. Water 10 quarts, neutral bisulphite of soda 8J ozs., 
"98- or 99-percent, potassium cyanide 7 ozs., crystallized car- 
bonate of soda 6 ozs., crystallized copper acetate 7 ozs. 

Dissolve the first mentioned three salts together in half the 
quantity of the water, and the acetate of copper in the other 
half, and pour the last solution into the first, stirring con- 
stantly. It is recommended to add to this bath 77 to 123 
grains of bisulphite of soda per quart. 



DEPOSITION OF COPPER, BRASS AND BRONZE. 331 

In preparing copper baths, the copper acetate prescribed in 
the preceding formulae may be replaced by the carbonate or 
sulphate, the substitution of the latter, after its previous con- 
version into carbonate, being of special advantage in order 
not to thicken the bath by the potassium sulphate formed by 
reciprocal decomposition. The following formula is especially 
suitable for the use of sulphate of copper (blue vitriol): 

IV. Blue vitriol 10J ozs. 

Crystallized carbonate of soda . . 10J ozs. 



Water 10 quarts. 

Pulverized bisulphite of soda ... 7 ozs. 
Crystallized carbonate of soda. . . 8J- ozs. 
98 to 99 per cent, potassium cyanide . 8| ozs. 

Electro-motive force at 10 cm. electrode-distance, about 3 
volts. 

Current-density, 0.35 ampere. 

First dissolve the 10J ozs. of blue vitriol and the lOf ozs. 
•of crystallized carbonate of soda, each by itself, in hot water, 
and mix the two solutions. Allow the precipitate of carbonate 
•of copper to settle, and pour off the supernatant clear fluid. 
Then pour upon the precipitate 5 quarts of water, add the 
bisulphite of soda, next the carbonate of soda, and mix this 
solution with the solution of the potassium cyanide in 5 
quarts of water. The fluid rapidly becomes clear and color- 
less, when it is boiled and filtered. 

V. Water 15 quarts, cupron (cuprous oxide) 3 \ ozs., 99 per 
-cent, potassium cyanide 10 \ ozs., bisulphite of soda 10 J ozs. 

Electro-motive force at 10 cm. electrode-distance, 2.8 volts. 

'Current-density, 0.3 ampere. 

For the preparation of the bath, dissolve the potassium 
•cyanide in about 3 quarts of the water (cold), stir in gradually 
the cupron, then add the solution of the bisulphite of soda in 
3 quarts of the water, and with the remaining 9 quarts of 
water make up the bath to 15 quarts. 

As previously mentioned, an addition of sulphites to the 



332 ELECTRO-DEPOSITION OF METALS. 

cuprous oxide solution is not required since no cyanogen 
escapes. However, in dissolving cuprous oxide in potassium 
cyanide there is formed, in addition to potassium-copper cya- 
nide, potassium hydroxide (caustic potash) the presence of 
which in the bath is for various reasons not desirable. A 
sufficient quantity of bisulphite of soda to convert the caustic 
potash into neutral potassium sulphite is therefore added,, 
while the corresponding portion of bisulphite is converted 
into neutral sodium bisulphite. A sufficient excess of bisul- 
phite of soda lor the exertion of the above-mentioned favor- 
able effects upon the coppering process remains behind. 

Dr. Langbein has introduced in the copper-plating industry 
the cupro-cupric sulphite. It dissolves in potassium cyanide 
without noticeable formation of cyanogen, since it contains 
more than the sufficient quantity of sulphurous acid required 
for the reduction of the portion of cupric oxide present. Suit- 
able formulas for copper baths with cupro-cupric sulphite are :. 

VI. Water 10 quarts, 99 per cent, potassium cyanide 8J 
ozs., ammonium soda If ozs., cupro-cupric sulphite 4^ ozs., o?y 

Via. Water 10 quarts, 60 per cent, potassium cyanide 14 
ozs., cupro-cupric sulphite 4^ ozs. 

Dissolve the salts in the order given, stirring constantly,, 
and then add the remaining 5 quarts of water. 

The deposits obtained in these baths are of a beautiful 
warm color, very adherent and dense. 

Pfanhauser recommends the following bath, in which 
separately prepared crystallized potassium-copper cyanide, in 
addition to suitable conducting salts, which are wanting in 
Hossauer's formula, is used : 

VII. Water 10 quarts, ammonia-soda 3J ozs., anhydrous, 
sodium sulphite 7 ozs., crystallized potassium-copper cyanide 
10J ozs., potassium cyanide 0.35 ozs. 

For the preparation of the bath the salts are to be dissolved 
in a suitable quantity of water, stirring constantly. 

Electro-motive force at an electrode distance of 15 cm., 2.7 
volts for iron, 3.2 volts for zinc. Current-density 0.3 ampere. 



DEPOSITION OF COPPER, BRASS AND BRONZE. 333 

For small zinc objects which are to be coppered in a basket, 
baths III, TV, and V, may be used, or those up to and in- 
cluding VII, which are to be heated and compounded with a 
small additional quantity of potassium cyanide. For the 
same purpose, Roseleur recommends the following bath : 

VIII. Water 10 quarts, neutral crystallized sodium sulphite 
If ozs., neutral copper acetate 8 ozs., 75-per cent, potassium 
■cyanide 12^ ozs., ammonia 3 ozs. 

The bath is prepared in the same manner as the baths given 
under formulas I to III. 

Prepared coppering salts. Combinations under various names 
(Schering : triple metal salts ; Langbein Co. : double metal 
salts) are now brought into commerce, and are quite conven- 
ient for the preparation of copper baths (and brass baths) in 
so far that only one weighing of the substance is required. 

As regards their composition these preparations are com- 
binations of potassium-copper cyanide (relatively potassium- 
rzinc cyanide) with alkaline sulphites, such as, for instance, are 
formed by dissolving cupro-cupric sulphite in potassium cya- 
nide and subsequent evaporation to dryness. As the copper 
•content in Langbein Co's. double copper salt amounts to from 
20 to 21 per cent., copper baths with any desired content of 
metal can in a very simple manner be prepared. Thus, for 
instance, a copper bath with 92.59 grains of copper per quart 
is obtained by dissolving 6.6 lbs. of double copper salt in 100 
quarts of water; and a copper bath with 138.88 grains of cop- 
per per quart, by dissolving 9.9 lbs. of double copper salt 
in 100 quarts of water. It may be added that there is very 
seldom occasion to exceed 138.88 grains of copper per liter. 

As these preparations can contain but a small content of free 
potassium cyanide to prevent them from absorbing moisture 
when stored, it is advisable to dissolve in the baths prepared 
from them 46 to 78 grains of 99-per cent, potassium cyanide. 
It has also proved of advantage to add certain conducting 
salts, for instance, neutral sodium sulphite, in order to effect 
a better anodal solution of the copper. 



334 ELECTRO-DEPOSITION OP METALS. 

A copper salt brought into commerce by the Hanson & Van? 
Winkle Qo. of Newark, N. J., under the name of ruby oxide r 
may to advantage be used in making copper solutions, it 
being claimed to give a much deeper red deposit than is 
possible to obtain with a carbonate solution. 

Copper baths without potassium cyanide. Of the many direc- 
tions for the preparation of these baths, only a few need here 
be mentioned. 

For coppering zinc objects, Roseleur recommends the follow- 
ing bath : 

IX. Water 10 quarts, tartar, free from lime, 6.7 ozs.,. 
crystallized carbonate of soda 15 ozs., blue vitriol 6.7 ozs.,. 
caustic soda lye of 16° Be., f lb. 

To prepare this bath, dissolve the tartar and the crystal- 
lized carbonate of soda in § of the water, and the blue vitriol 
in the remaining J, and mix both solutions. Filter off the 
precipitate, dissolve it in the caustic soda lye, and add this- 
solution to the other. 

This bath works very well, and may be recommended to- 
electro-platers who copper zinc exclusively ; though even for 
this purpose the baths prepared according to III, IV and V 
answer equally well. 

Weill obtains a deposit of copper in a bath consisting of a 
solution of blue vitriol in an alkaline solution of tartrate ot 
potassium or sodium. Such a bath is composed as follows : 

X. Water 10 quarts, potassium sodium tartrate (Rochelle 
salt) 53 ozs., blue vitriol 10J ozs., 60 per cent, caustic soda 
28 ozs. 

The chief purpose of the large content of caustic soda is to 
keep the tartrate of copper, which is almost insoluble in water, 
in solution. According to Weill, the coppering may be exe- 
cuted in three different ways, as follows: 

The iron articles tied to zinc wires, or in contact with zinc 
strips, are brought into the bath ; the coppering thus taking 
place by contact. Or, porous clay cups are placed in the 
bath containing the articles ; these clay cups are filled with 



DEPOSITION OP COPPER, BRASS AND BRONZE. 335 

soda lye in which zinc plates connected with the object-rods 
are allowed to dip, the arrangement in this case forming a 
cell with which, by the solution of the zinc in the soda lye, a 
current is produced, which affects the decomposition of the 
copper solution and the deposition. When saturated with 
zinc the soda lye becomes ineffective, and, according to Weill, 
it may be regenerated by the addition of sodium sulphite, 
which separates the dissolved zinc as zinc sulphide. The third 
method of coppering consists in the use of the current of a bat- 
tery or of a dynamo machine, in which case copper anodes 
have, of course, to be employed. According to the method 
used, coppering is effected in a shorter or longer time. In 
contact-coppering at least six hours were required for the pro- 
duction of a tolerably heavy deposit, and with the use of a 
current generated by an external source, no other advantage 
of this bath over potassium-copper cyanide baths could be 
noticed than that being free from potassium cyanide, it is not 
poisonous. However, the danger in the use of copper cyanide 
baths is generally overestimated by the layman, there being 
actually none, if proper care be observed. 

Another copper bath, recommended by Walenn, consists of 
a solution of equal parts of neutral tartrate of ammonia and 
potassium cyanide, in which 3 to 5 per cent, of copper (in the 
form of blue vitriol or moist cupric hydrate) is dissolved. The 
bath is to be heated to about 140° F. 

Gauduin's copper bath consists of a solution of oxalate of 
copper with oxalate of ammonia and free oxalic acid. Fon- 
taine asserts that the bath works well when heated to between 
140° and 150° F. 

Tanks for potassium-copper cyanide baths. Copper baths con- 
taining cyanide cannot be brought into pitched tanks, tanks of 
stoneware or enameled iron being used for smaller baths, and 
for larger ones, basins of brick set in cement, or iron reservoirs 
lined with cement. Wooden tanks lined with celluloid are 
also useful. For large baths containing potassium cyanide 
wooden tanks lined with lead can be used without disadvan- 



336 ELECTRO-DEPOSITION OF METALS. 

tage, since a slight coating of cyanide of lead which may be 
formed upon the lead is insoluble in potassium cyanide, and 
even if a small quantity of cyanide of lead would be dissolved 
in the bath by the presence of organic acids, a separation of 
lead besides copper upon the cathodes does not take place. 

Copper anodes. For this purpose it is best to use annealed 
sheets of pure copper about 0.11 to 0.19 inch thick. They 
should first be for some time pickled in dilute sulphuric acid, 
and then scratch-brushed, in order to give them a pure metal- 
lic surface. 

The anode-surface should be as large as possible, at least as 
large as the object-surface suspended in the bath. 

In all baths containing cyanide the anodes become in a 
comparatively short time coated with a greenish slime which 
consists of basic cuprous cyanide, and is mostly soluble in 
excess of potassium cyanide. When a very thick formation 
•of such slime takes place, potassium cyanide is wanting and 
dias to be added. 

In addition to this coat of cuprous c} T anide, there may also 
be formed upon the anode a brown film of paracyanide which 
adheres very tenaciously and cannot be removed with potas- 
sium cyanide, but has to be taken off by scratch-brushing or 
scouring with pumice. When coppering with small anode- 
surfaces, and potassium cyanide is at the same time wanting, 
the coat may become so thick that no current passes into the 
bath, and consequently no deposit is formed. This feature 
may even appear when the bath contains a sufficient excess 
•of potassium cyanide, because the cyanide formed in abund- 
ance on the anode by high current-densities cannot with 
sufficient rapidity be dissolved by the potassium cyanide. In 
this case, recourse must also be had to scouring the anodes, 
and then increasing the anode-surfaces. The anodes are best 
suspended to the anode-rods by means of copper bands riveted 
on. 

Execution of copper-plating. — The general rules given under 
nickeling, as regards the suitable composition of the bath, 



DEPOSITION OF COPPER, BRASS AND BRONZE. 337 

correct selection of anodes, careful scouring and pickling of 
the objects, and proper current-strength also apply to copper- 
plating. 

In copper baths containing cyanide, too large an excess of 
potassium cyanide, to be sure, produces an evolution of hydro- 
gen-bubbles on the objects, but it yields either no deposit at 
all or only a slight one, which readily peels off. If this phe- 
nomenon is noticed after an addition of potassium cyanide is 
made, the excess has to be removed by adding a copper salt, 
best, cupro-cupric cyanide. For this purpose triturate the 
latter with a small quantity of the copper bath in a small por- 
celain mortar to a thinly-fluid paste, and add the latter to the 
bath, stirring vigorously for some time. After each addition, 
see whether an object suspended in the bath becomes rapidly 
and properly coppered and, if such be not the case, repeat 
the addition of cupro-cupric cyanide until the bath works in 
a faultless and correct manner. 

However, deposition may also fail by reason of an insuffi- 
cient addition of potassium cyanide. This is recognized by 
the heavy formation of froth on the anodes and the appear- 
ance of a pale blue color in the fluid, though this may also be 
caused by the content of metal in the bath being too small. 
While in the first case, the simple addition of 15 to 30 grains 
of potassium cyanide per quart will cause the bath to deposit 
in the proper manner, in the second case, solution of copper 
cyanide in potassium cyanide is required in order to increase 
the content of metal, and it is advisable to add at the same 
time a small quantity of carbonate of soda and of bisulphite 
of soda. In place of preparing a solution of copper cyanide 
in potassium cyanide, it is recommended to use crystallized 
copper cyanide, which can be obtained from manufacturers of 
chemicals, and dissolve it in hot water. 

Many platers are of the opinion that the articles to be 
copper-plated do not require very careful cleaning and pick- 
ling before plating, because this is supposed to be sufficiently 
effected by the baths themselves, by those containing potas- 
22 



338 ELECTRO-DEPOSITION OF METALS. 

sium cyanide, as well as by those with alkaline organic com- 
binations. This opinion, however, is wrong. It is true the 
potassium cyanide dissolves a layer of oxide, but not, or at 
least very incompletely, any grease present upon the articles, 
and hence it is advisable to free objects intended for coppering 
as thoroughly from grease as those to be nickeled. 

The preliminary scouring and pickling of the articles to be 
coppered are executed according to the directions given on p. 
223. The same precautions referred to under " Deposition of 
Nickel " have to be used in suspending the objects in the bath, 
and the directions given there for the suitable arrangement of 
the anodes, etc., also apply to coppering. However, as a cop- 
per bath conducts better than a nickel bath, the distances 
between the anodes and the objects may, if necessary, be some- 
what greater. 

With a proper arrangement of the anodes and correct regu- 
lation of the current, the objects should be entirely coated 
with copper in a few minutes after being suspended in the 
bath. In five to ten minutes the objects are taken from the 
bath and brushed with a scratch-brush of not too hard brass 
wires, whereby the deposit should everywhere show itself to 
be durable and adherent. Defective places are thoroughly 
scratch-brushed, scoured, and pickled ; the objects are then re- 
turned to the bath. For solid and heavy plating, the objects 
remain in the bath until the original luster and red tone of 
the coppering disappear and pass into a dull, discolored 
brown. At this stage the objects are again scratch-brushed 
until they show luster and the red copper color, and in doing 
this it is of advantage to moisten them with tartar water. 
They are then again returned to the bath, where they remain 
until the dull, discolored tone reappears. They are then 
taken out, scratch-brushed bright, rinsed in several clean 
waters, plunged into hot water, and finally dried, first in saw- 
dust and then thoroughly, at a high temperature, in the dry- 
ing chamber. 

Special attention must be paid to the thorough washing o 



DEPOSITION OF COPPEE, BRASS AND BRONZE. 339 

the coppered objects, because, if a trace of the bath containing 
cyanide remains in the depressions or pores, small, dark, round 
stains appear on those places, which cannot be removed, or at 
least only with great difficulty, they reappearing again in a 
short time after having been apparently removed. This for- 
mation of stains appears most frequently upon coppered (as 
well as brassed) iron and zinc castings, which cannot be pro- 
duced without pores. To prevent the formation of these stains 
the following method is recommended : Since the rinsing in 
many waters, and even allowing the objects to lie for hours in 
running water, offer no guarantee that every trace of fluid 
containing cyanide has been removed, the objects are brought 
into a slightly acid bath which decomposes the fluid, a mix- 
ture of 1 part of acetic acid and 50 parts of water being well 
adapted for the purpose. The objects are allowed to remain 
in this mixture for three to five minutes, when they are rinsed 
off in water and dipped for a few minutes in dilute milk of 
lime. They are finally rinsed and dried. Coppered castings 
thus treated will in most cases show no stains. 

0. Shultz obtained a patent for the following method for 
removing the hydrochloric acid from the pores, and for pre- 
venting the formation of stains: The plated objects are placed 
in a room which can be hermetically closed. The air is then 
removed from the room by the introduction of steam of a high 
tension and by means of an air-pump, and water is sprinkled 
upon the objects. By this treatment in vacuum the fluid 
in the pores comes to the surface, and the salt solution is 
removed by the water sprinkled over the articles. 

After drying, the deposit of copper, if it is to show high 
luster, is polished upon soft wheels of fine flannel and dry 
Vienna lime. Commercial rouge FFF, moistened with a lit- 
tle alcohol, is also an excellent polishing agent for copper and 
all other soft metals. 

As is well known, massive copper rapidly oxidizes in a 
humid atmosphere, and this is the case to a still greater 
extent with electro-deposited copper. Hence, the coppered 



340 ELECTRO-DEPOSITION OF METALS. 

objects, if they are not to be further coated with a non-oxi- 
dizing metal, have to be provided with a colorless, transparent 
coat of lacquer. 

It frequently happens that slightly coppered (as well as 
slightly brassed) objects, especially of zinc, after some time, 
become entirely white and show no trace of the deposit. 
This is due to the deposit penetrating into the basis-metal, as 
already explained. Lacquering in this case is of no avail, 
the deposit also disappearing under the coat of lacquer. The 
only remedy against this phenomenon is a heavier deposit. 

If the coppered objects are to be coated with another metal, 
drying is omitted, and after careful rinsing they are directly 
brought into the respective bath, or into the quicking pickle, 
if, as for instance, in silvering, quicking has to be done. In 
such cases, where the copper deposit serves only as an inter- 
mediary for the reception of another metallic coating, the 
objects need not be coppered as thickly, as previously de- 
scribed, by treating them three times in the bath. Prelimi- 
nary coppering for 5 to 10 minutes suffices in all cases, which 
is succeeded by scratch-brushing in order to be convinced 
that the deposit adheres firmly, and that the basis-metal is 
uniformly coated. The objects are then suspended in the 
bath for from 5 to 10 minutes longer with a weak current. 

In coppering sheet-iron or sheet-zinc which is to be nickeled, 
the sheets are taken from the bath after 3 to 5 minutes, at any 
rate while they still retain luster, scratch-brushing being in 
this case omitted. For coppering such sheets a current-density 
of 0.5 ampere and an electro-motive force of 3.5 to 4 volts is 
required. 

The treatment of copper baths when they become inactive, 
or show other abnormal features, has already been referred to. 

When, as is frequently done, a fluid prepared by dissolving 
cuprous oxide in potassium cyanide is used in place of solu- 
tion of crystallized potassium copper cyanide in water, for 
increasing the content of metal, it must not be forgotten to 
add the corresponding quantity of bisulphite of soda for the 



DEPOSITION OF COPPER, BRASS AND BRONZE. 341 

conversion of the caustic potash formed into potassium 
sulphate. 

All other general rules for plating baths given under 
" Electro-plating Solutions," Chapter V., must here also be 
observed. 

In the course of time, copper-cyanide baths become thick in 
consequence of the decomposition of the potassium cyanide 
and the accumulation of alkaline carbonate and other products 
of transformation formed thereby, the additions for refreshing 
the baths also partly contributing thereto. While the normal 
specific gravity of freshly prepared baths is, according to their 
composition, from 5° to 7° Be., the baths after having been in 
operation for several years may show 11 ° Be. and more. It is 
frequently found that coppering in baths which have become 
thick is not effectual, the deposit not adhering so well and not 
showing the brilliant color of copper "as when produced in a 
fresh bath. The only remedy for this is diluting the bath 
with water to 6° or 7° Be., increasing the content of metal 
by adding highly concentrated solution of potassium copper 
cyanide, and decomposing the alkaline carbonates, or at least 
a greater portion of them, by conducting sulphurous acid into 
the bath, or by dissolving bisulphite of soda in it. 

Coppering small articles in quantities. If a large quantity of 
small articles is at one time to be coppered in dipping baskets, 
it is recommended to use the baths quite hot, this causing, to 
be sure, a considerably larger consumption of potassium cya- 
nide than in cold baths. For the rest the process is the same 
as that given for nickeling small objects in quantities. 

If very large quantities of small articles have continually 
to be coppered, one of the mechanical plating contrivances 
referred to in Chapter VI will do good service. 

The inlaying of depressions of coppered art-castings with 
black may be done in different ways. Some blacken the 
ground by applying a mixture of spirit lacquer with lamp- 
black and graphite, while others use oil of turpentine with 
lampblack and a few drops of copal lacquer. A very thin 



342 ELECTRO-DEPOSITION OF METALS. 

nigrosin lacquer mixed with finely pulverized graphite is very- 
suitable for the purpose. When the lacquer is dry the ele- 
vated places which are to show the copper color are cleansed 
with a linen rag moistened with alcohol. 

Electrolytically coppered articles may be inlaid black by 
coating them, after thorough scouring and pickling, with 
arsenic in one of the baths given under " Electro-deposition of 
Arsenic," and-, after drying in hot water and sawdust, freeing 
the surfaces and profiles, which are to appear coppered, from 
the coating of arsenic by polishing upon a felt wheel. If this 
polishing is to be avoided, the portions which are not to be 
black may be coated with stopping-off varnish, and arsenic 
deposited upon the places left free. 

For coppering by contact and boiling, see special chapter, 

" Depositions by Contact." 

For coloring, patinizing and oxidizing of copper, see the proper 
chapter. 

Examination of Copper Baths Containing Potassium Cyanide. 

In the preceding sections several characteristic indications 
which serve for the qualitative examination of these baths have 
already been given. Like all baths containing potassium 
cyanide, their original composition gradually suffers extensive 
alterations by the decomposition of the potassium cyanide, 
which by the carbonic acid of the air is changed to potassium 
carbonate and hydrogen cyanide, and spontaneously also to 
ammonia and potassium formate. The potassium cyanide is 
also split up by the current, potassium hydroxide being 
formed, together with decomposition of water, which by the 
carbonic acid of the air is gradually converted into potash, 
while hydrogen cyanide and hydrogen escape. Under certain 
conditions an oxidation of the potassium cyanide to potassium 
cyanite may also take place. 

The excess of potassium cyanide required for the correct 
performance of the copper bath is therefore gradually con 
sumed, and the bath, at first of a wine-yellow color, acquires 



DEPOSITION OF COPPER, BRASS AND BRONZE. 343 

a blue coloration, and does no longer yield a good deposit. 
When such is the case, the same quantity of copper which is 
withdrawn from the bath by the deposit is not dissolved from 
the anodes, and hence the determination of the content of free 
potassium cyanide, as well as that of the content of copper, 
may at times be necessary. A determination of the potassium 
carbonate (potash) formed in the bath and its removal, or 
conversion into potassium cyanide by the addition of the cor- 
responding quantity of barium cyanide solution, which will be 
referred to under silver baths cannot be recommended. This 
determination in copper baths which contain, as is generally 
the case, sulphides, is troublesome, and an accumulation of 
potash in copper baths does not produce the same evils as in 
a silver bath. If, however, a copper bath, after working for 
years, has become thick in consequence of a large content of 
potash, it can be renewed without considerable expense, or, if 
this is not desired, it can be regenerated by diluting with 
water, and increasing the content of copper and of potassium 
cyanide. 

Hence, the determination of the free potassium cyanide 
(i. e., not fixed on copper) and that of the copper will here 
only be discussed. 

Determination, of potassium cyanide. — The best and most 
rapid method for this purpose is by titrating with decinormal 
solution of silver nitrate. Silver nitrate and potassium cyanide 
form finally potassium nitrate and insoluble silver cyanide, the 
latter, however, being redissolved to potassium silver cyanide 
so long as free potassium cyanide is present. Since potassium 
silver cyanide contains two molecules of cyanogen, one mole- 
cule of silver nitrate corresponds to two molecules of potassium 
cyanide, and 1 cubic centimeter of decinormal solution of sil- 
ver nitrate corresponds to 0.013 gramme of potassium cyanide. 

Bring, by means of a pipette, 5 cubic centimeters of the 
copper bath into a beaker having a capacity of about J liter. 
Dilute with about 150 cubic centimeters of water, add one or 
two drops of saturated common salt solution, and then, whilst 



344 ELECTRO-DEPOSITION OF METALS. 

constantly stirring the fluid in the beaker, allow to flow in from 
the burette silver nitrate solution so long as the precipitate 
formed dissolves rapidly. 

When solution becomes sluggish, add, stirring constantly*- 
silver nitrate solution drop by drop, waiting after the addition 
of each drop until the fluid has again become clear. When 
the fluid does not become clear after adding the last drop, and 
it shows a slight turbidity, no more free potassium cyanide is 
present. By multiplying the cubic centimeters of decinormal 
solution of silver nitrate used by 2.6 the content of potassium 
cyanide per liter of bath is found. 

Suppose, for instance, for 5 cubic centimeters of bath, 2.2: 
cubic centimeters of silver solution have been used, then 1 
liter of the bath contains 2.2 X 2.6 = 5.72 grammes of free' 
potassium cyanide, because 1 cubic centimeter of silver solu- 
tion corresponds to 0.013 grammes of potassium cyanide, 
therefore 2.2 cubic centimeters = 2.2 X 0.013 = 0.028$ 
grammes, from which results by calculation 

5 : 0.0286 = 100 : x 



x — 5.72 grammes. 

If now the initial content of free potassium cyanide in the 
freshly prepared bath has been determined, a later determina- 
tion will show the deficiency of it which has come about. It 
must, however, be taken into consideration that the potassium 
formate formed by the decomposition of the potassium cyanide 
may, up to a certain degree, apparently fill the role of the 
potassium cyanide, in so far as it decreases the conducting re- 
sistance of the bath, but it does not contribute to the solution 
of the anodes. Hence, if the established deficiency of potas- 
sium cyanide would be replaced by equally large quantities of 
the salt, there would be danger of too much of it getting into 
the bath, and the latter would conduct too readily, which 
would result in the deposit precipitating too rapidly and 
turning out less adherent. 



DErOSITION OF COPPER, BRASS AND BRONZE. 345 

Hence it is evident that analytical methods alone are not 
sufficient for maintaining entirely constant baths containing 
potassium cyanide, and practical experience and a good fac- 
ulty of observation are required if the results of analysis are 
to be utilized for the correction of the baths. The potassium 
formate can neither be removed from the bath nor can it be 
quantitatively determined, and since its action in the bath is 
not accurately known, it can only be stated from practical 
experience, that under normal conditions only about 60 per 
cent, of the deficiency of free potassium cyanide in a copper 
bath should be replaced by pure potassium cyanide. 

Determination of copper. This may be effected by electro- 
lytic or volumetric analysis. 

For the determination of copper by electrolysis, measure off by 
means of the pipette, 10 cubic centimeters of the copper bath,, 
and allow the fluid to run into a porcelain dish having a ca- 
pacity of 150 to 200 cubic centimeters. Add 10 cubic centi- 
meters of pure, strong hydrochloric acid, cover the dish with a 
watch-glass and heat upon the water-bath. When evolution of 
gas ceases, carefully remove the watch-glass, rinse off adhering 
drops with a small quantity of distilled water into the dish, and 
evaporate the contents of the latter nearly to dryness. Now add 
about 1 cubic centimeter of strong nitric acid, swing the dish to 
and fro so that all portions of the residue are moistened by the 
acid, heat for a short time, and then add 32 cubic centimeters- 
of pure dilute sulphuric acid (1 part acid, 2 parts water), with 
which the contents of each dish are heated, until every trace of 
odor of hydrochloric and nitric acids has disappeared. Now 
pour the copper solution into the platinum dish serving for 
electrolysis, rinse the porcelain dish with distilled water, add- 
ing the wash-water to the contents of the platinum dish, fill 
the latter up to within 1 centimeter of the rim with water, 
add 2 cubic centimeters of pure concentrated nitric acid, and 
electrolyze with a current-strength of ND 100 = 1 ampere, i. e. r . 
1 ampere for 100 square centimeters surface of the platinum, 
dish which serves as cathode. 



346 ELECTRO-DEPOSITION OF METALS. 

The copper separates with a bright red color, adhering 
firmly to the platinum dish, which is connected with the neg- 
ative pole of the source of current. That the separation of 
copper is finished is recognized by a narrow strip of platinum 
sheet, when suspended in the platinum dish, showing in 15 
minutes no trace of coppering ; or by a few drops of the solu- 
tion when brought together with a drop of yellow prussiate of 
potash solution, producing no red coloration. 

When by one of the above-mentioned means the complete 
separation of the copper has been ascertained, the platinum 
dish is washed, without interruption of the current, the water 
removed b} r rinsing the dish with absolute alcohol, and the 
latter removed by rinsing with ether. Dry for a short time in 
an air-bath at 212° F., and weigh the dish together with the 
precipitate of copper. By deducting the weight of the dish, 
the weight of the copper is obtained, and, since 10 cubic centi- 
meters of the bath were electrolyzed, the weight of the copper 
multiplied by 100 gives the contents of copper in grammes in 
1 liter of copper bath. 

The volumetric determination of copper is based upon the 
principle that solution of sulphate or chloride of copper forms 
with potassium iodide, copper iodide, whilst free iodine is at 
the same time formed, one atom of liberated iodine corres- 
ponding to one molecule of copper salt. This free iodine is 
determined by titration with a solution of sodium hyposulphite 
of known content, and the content of copper is calculated from 
the number of cubic centimeters of the solution used. For the 
recognition of the final reaction, the blue coloration, which 
originates when starch solution combines with free iodine, is 
utilized. There are required a decinormal iodine solution 
which contains per liter exactty 12.7 grammes of re-sublimated 
iodine dissolved in potassium iodide, and a decinormal solu- 
tion of sodium hyposulphite, of which 10 cubic centimeters 
diluted with water and compounded with a small quantity 
of starch solution must exactly use 10 cubic centimeters of 
iodine solution to give a permanent blue coloration by the 
formation of iodine-starch. 



DEPOSITION OF COPPER, BRASS AND BRONZE. 347 

The mode of operation is as follows : Heat in a porcelain 
•dish 10 cubic centimeters of the copper bath with 10 cubic 
centimeters of strong hydrochloric acid, evaporate nearly to 
dryness with 1 cubic centimeter of strong nitric acid and 2 
cubic centimeters of hydrochloric acid, and heat upon the 
water-bath until the nitric acid is entirely removed. The resi- 
due is dissolved in water with the addition of a small quantity 
of dilute hydrochloric acid. The clear solution is brought into 
a measuring flask holding 100 cubic centimeters, the dish is 
rinsed with water, the free acid neutralized by the addition of 
dilute soda lye until a precipitate of bluish copper hydrate 
commences to separate, which after vigorous shaking does not 
disappear. Now add, drop by drop, hydrochloric acid until 
the precipitate just dissolves, fill the flask up to the 100-centi- 
meter mark with water, and mix by shaking. Of this solu- 
tion bring by means of the pipette, 10 cubic centimeters into 
a glass of 100 cubic centimeters capacity, and provided with 
a glass stopper, add 10 cubic centimeters of a 10 per cent, 
.potassium iodide solution, dilute with a small quantity of 
water, close the glass with the stopper, and let it stand for 10 
minutes. Now add from a burette, decinormal solution of 
sodium hyposulphite until the iodine solution has become 
colorless, and then add a few cubic centimeters more. Next 
bring into the flask a few drops of starch solution, and then 
add from another burette, decinormal iodine solution until a 
l)lue coloration is just perceptible. By deducting the cubic 
•centimeters of iodine solution used from the cubic centimeters 
of sodium hyposulphite solution, it will be known how many 
cubic centimeters of the latter solution have been used for 
fixing the iodine liberated by the reciprocal action between 
copper solution and potassium cyanide solution. Since 1 cubic 
•centimeter of a sodium hyposulphite solution, which is equiva- 
lent to the decinormal iodine solution, corresponds to 0.0063 
gramme of copper, therefore, as 1 cubic centimeter of the bath 
has been titrated, the number of cubic centimeters found has 
to be multiplied by 6.3 to find the content of copper per liter 
of copper bath. 



348 ELECTRO-DEPOSITION OF METALS. 

Suppose to 10 cubic centimeters of the copper solution 
mixed with potassium iodide has been added 2.8 cubic centi- 
meters of sodium hyposulphite solution, and for titrating back 
the excess 0.7 cubic centimeters of iodine solution had been 
used up to the appearance of the blue coloration, then 2.8 — 
0.7 = 2.1 centimeters have been used, which multiplied by 
6.3 gives 13.23 grammes as the content of copper per liter of 
bath. 

If now a deficiency of copper has been established by one 
or the other method, the original content of copper can be 
readily restored by the addition of crystallized potassium- 
copper cyanide. This salt, when pure, contains about 30 per 
cent, copper. 

Suppose, when first prepared, the bath contained 15 grammes 
of copper per liter, and it has been shown by analysis that it 
now contains only 13.3 grammes, then a deficiency of 1.7 
grammes of copper has to be made up. Since 100 grammes 
of potassium-copper cyanide contain 30 grammes of copper,, 
then 

3 : 100 = 1.7 :x 
~~~x = 3.57 

and hence 3.57 grammes of potassium-copper cyanide per liter 
have to be dissolved in the bath. It is advisable to electro- 
lytically determine in the previously described manner, after 
first destroying the cyanogen combinations, the content of 
copper in the potassium-copper cyanide to be used for strength- 
ening the bath, so that in case the salt shows a smaller con- 
tent of copper, the proper quantit} 7 of it may be added. 

2. Deposition of Brass. 
Brass is an alloy of copper and zinc, whose color depends 
on the quantitative proportions of both metals. The alloys 
known as yellow brass, red brass (similor, tombac), consist es- 
sentially of copper and zinc, while those known as bell metal T 
gun metal, and the bronzes of the ancients are composed of copper 
and tin. Modern bronzes contain copper, zinc and tin. 



DEPOSITION OF COPPER, BRASS AND BRONZE. 349 

The behavior of brass towards acids is nearly the same as 
that of copper. It oxidizes, however, less rapidly in the air, 
is harder than copper, malleable, and can be rolled and drawn 
into wire. 

Brass baths. In accordance with the plan pursued in this 
work only the most approved formulas, the greater portion of 
which has been practically tested, will be given. More recent 
propositions which cannot be recognized as improvements 
over the older directions, will be critically commented upon. 
There is a large number of receipts for brass baths which 
show such remarkable difference in the proportions of the two 
metals that, on more closely examining them, even the layman 
can, at the first glance, discover the doubtful result. Thus, 
for instance, Russell and Woolrich recommend a bath in 
which the quantity of copper salt to zinc salt is in the pro- 
portion of 10:1. Other authors give the following propor- 
tions : Copper 1 to zinc 8 (Heeren) ; copper 1 to zinc 2 (Sal- 
zede, Kruel); copper 2 to zinc 1 (Newton). These examples 
will show the difference of opinion regarding the suitable 
■composition' of brass baths. 

An electro-plater understanding all the conditions and the 
effect of the current-strength might possibly obtain a deposit 
of brass even from baths which show such abnormal propor- 
tions of mixture as those made up according to the directions 
by Russell, Heeren, and others, but how many conditions have 
thereby to be taken into consideration will be shown later on. 
We share the opinion of Roseleur that a brass bath containing 
copper and zinc salts in nearly equal proportions is the most 
suitable and least subject to disturbances. A brass bath is to 
be considered as a mixture of solutions of copper cyanide and 
zinc cyanide, or of other copper-zinc salts, in the most suitable 
solvent. Now, since a solution of copper cyanide requires a 
different current-strength from one of zinc salt, it will be seen 
that according to the greater or smaller current-strength, now 
more of the one, and now more of the other, metal is depos- 
ited, which, of course, influences the color of the deposit. 



350 ELECTRO-DEPOSITION OF METALS. 

Hence the proper regulation of the current is the chief condi- 
tion for obtaining beautiful deposits, let the bath be composed 
as it may. 

For all baths containing more than one metal in solution, it 
may be laid down as a rule that the less positive metal is first 
deposited. In a brass bath, copper is the negative, and zinc 
the positive metal ; and hence a weaker current deposits more 
copper, in consequence of which the deposit becomes redder, 
while, vice versa, a more powerful current decomposes, in addi- 
tion to the copper solution, also a larger quantity of zinc solu- 
tion, and reduces zinc, the color produced being more pale 
yellow to greenish. By bearing this in mind it is not difficult 
to obtain any desired shades within certain limits. 

I. Brass bath according to Roseleur. — Blue vitriol and zinc 
sulphate (white vitriol), of each 5J ounces, and crystallized 
carbonate of soda 15f ounces. Crystallized carbonate of 
soda and bisulphite of soda in powder, of each 7 ounces, 98 
per cent, potassium cyanide 8f ounces, arsenious acid 30f 
grains, water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 2.6 to 2.8- 
volts. 

Current-density, 0.32 ampere. 

The bath is prepared as follows : In 5 quarts of warm water 
dissolve the blue vitriol and the zinc sulphate ; and in the 
other 5 quarts the 15f ounces of carbonate of soda ; then mix 
both solutions, stirring constantly. A precipitate of car- 
bonate of copper and carbonate of zinc is formed, which is 
allowed quietly to settle for 10 to 12 hours, when the super- 
natant clear fluid is carefully poured off, so that nothing of 
the precipitate is lost. Washing the precipitate is not neces- 
sary. The clear fluid poured off is of no value and is thrown 
away. Now add to the precipitate so much water that the 
resulting fluid amounts to about 6 quarts, and dissolve in it, 
with constant stirring, the carbonate and bisulphite of soda, 
adding these salts, however, not at once, but gradually, in 
small portions, to avoid foaming over by the escaping car- 



DEPOSITION OF COPPER, BRASS AND BRONZE. 351 

bonic acid. Dissolve the potassium cyanide in 4 quarts of 
cold water and add this solution, with the exception of about 
| pint in which the arsenious acid is dissolved with the assist- 
ance of heat, to the first solutions, and finally add the solution 
of arsenious acid in the J pint of water retained, when the 
bath should be clear and colorless. If after continued stir- 
ring, particles of the precipitate remain undissolved, carefully 
add somewhat more potassium cyanide until solution is 
complete. 

The addition of a small quantity of arsenious acid is claimed 
to make the brassing brighter ; but the above-mentioned pro- 
portion of 30f grains for a 10-quart bath must not be ex- 
ceeded, as otherwise the color of the deposit would be too 
light and show a gray tone. 

II. Crystallized carbonate of soda 10J ounces, pulverized 
bisulphite of soda 7 ounces, neutral copper acetate 4.4 ounces, 
pulverized chloride of zinc 4.4 ounces, 98-per cent, potassium 
cyanide 14.11 ounces, arsenious acid 30f grains, water ]0 
quarts. 

Electro-motive force at 10 cm. electrode-distance 2.6 to 2.8 
volts. 

Current density 0.32 ampere. 

The preparation of this bath is more simple than that of the 
preceding. 

Dissolve the carbonate and bisulphite of soda in 4 quarts of 
water, then mix the acetate of copper and chloride of zinc with 
2 quarts of water, and gradually add this mixture to the solu- 
tion of the soda salts. Next dissolve the potassium cyanide in 
4 quarts of water, and add this solution to the first, retaining, 
however, a small portion of it, in which dissolve the arsenious 
acid with the assistance of heat. Finally add the arsenious 
acid solution, when the bath will become clear. If, however, 
the solution should not be clear and colorless, or at least wine- 
yellow, after adding the potassium cyanide, an additional 
small quantity of the latter may be used, avoiding, however, 
a considerable excess. 



352 ELECTRO-DEPOSITION OF METALS. 

For brassing iron in this bath, the quantity of carbonate of 
soda may be increased up to 35 ozs. for a 10-quart bath. This 
is also permissible, when in plating zinc articles with a heavy 
deposit of brass, frequent scratch-brushing is to be avoided. 
It would seem that a large content of carbonate of soda in the 
bath retards to a considerable extent the brass color from 
changing into a discolored brown, though the brilliancy of the 
deposit appears to suffer somewhat. When boiled for 1 to 2 
hours, or worked through with the current for 10 to 12 hours, 
the bath prepared according to formula II. works very well. 

Cupro-cupric sulphide and cuprous oxide may also be ad- 
vantageously used for the preparation of brass baths. Suitable 
formulas for them are as follows : 

Ilcr. Pure crystallized zinc sulphate (zinc vitriol or white 
vitriol) 5§- ozs., crystallized carbonate of soda 7 ozs., pulverized 
bisulphite of soda 4^ ozs., ammonium-soda 5^ ozs., 99 per 
cent, potassium cyanide 10 \ ozs., cupro-cupric sulphide 3-g- 
ozs., water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 2.8 volts. 

Current- density, 0.5 ampere. 

The bath is prepared as follows : Dissolve the zinc sulphate 
in 5 quarts of water and the crystallized carbonate of soda in 
4 quarts of warm water, and mix the two solutions. When 
the precipitate of zinc carbonate, which is formed, has com- 
pletely settled, siphon off the supernatant fluid as much as 
possible, and throw the lye away. 

Dissolve the bisulphite of soda, the ammonium-soda, and 
the potassium cyanide in 5 quarts of water, add the cupro- 
cupric sulphide, stirring constantly, and when solution is com- 
plete, add the precipitate of zinc carbonate. 

This bath yields beautiful pale yellow deposits of a warm 
brass tone. 

116. Potassium cyanide 10J ozs., cuprous oxide 3 ozs., zinc 
• chloride 2| ozs., bisulphite of soda 7 ozs., water 10 quarts. 

Dissolve the potassium cyanide in 5 quarts of water, add 
tthe cuprous oxide and stir until solution is complete. Dis- 



DEPOSITION OF COPPER, BRASS AND BRONZE. 353 

solve the bisulphite of soda and the zinc chloride in the other 5 
quarts of water, and mix the two solutions, stirring vigorously. 
If metallic cyanides are to be used for the preparation of 
brass baths, the following formula may be recommended : 

III. Crystallized carbonate of soda 10J ozs., pulverized 
bisulphite of soda 7 ozs., copper cyanide and zinc cyanide of 
each 3 J ozs., water 10 quarts, and enough 98 per cent, potas- 
sium cyanide to render the solution clear. 

To prepare the bath dissolve the carbonate 1 and bisulphite 
of soda in 2 or 3 quarts of water, rub in a porcelain mortar 
the copper cyanide and zinc cyanide with a quart of water to 
a thin paste, add this paste to the solution of the soda salts, 
and finally add, with vigorous stirring, concentrated potas- 
sium cyanide solution until the metallic cyanides are dissolved. 
Dilute the volume to 10 quarts, and, for the rest, proceed as 
given for formulas I and II. 

Brass baths may in a still more simple manner be prepared 
by using the double cyanides, potassium-cupric cyanide and 
potassium-zinc cyanide. 

Ilia. Potassium-cupric cyanide (crystallized) 5£ ozs., potas- 
sium-zinc cyanide (crystallized) 5f ozs., crystallized bisul- 
phite of soda 8f ozs., 98 per cent, potassium cyanide 11^ 
•drachms, water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 3 volts. 

Current- density, 0.3 ampere. 

The bath is prepared by simply dissolving the salts in warm 
water of about 122° F. 

For brassing zinc exclusively, Roseleur recommends the fol- 
lowing bath : 

IV. Dissolve 9| ozs. of crystallized bisulphite of soda and 
14 ozs. of 70 per cent, potassium cyanide in 8 quarts of water, 
and add to this solution one of 4| ozs. each of neutral copper 
acetate and crystallized chloride of zinc, 5|- ozs. of aqua am- 
monia of 0.910 specific gravity, and 2 quarts of water. 

For brassing wrought-iron, cast-iron and steel, Gore highly 
recommends the following composition : 
23 



354 ELECTRO-DEPOSITION OF METALS. 

IVa. Dissolve 35^ ozs. of crystallized carbonate of soda, 7 
ozs. of pulverized bisulphite of soda, 13| ozs. of 98 per cent, 
potassium cyanide in 8 quarts of water ; then add, stirring 
constantly, a solution of fused chloride of zinc 3J ozs., and 
neutral copper acetate 4J ozs., in 2 quarts of water. Boil and 
filter. The bath works well, best with an electro-motive force 
of 3.75 volts, and also takes readily on cast-iron. 

A solution for transferring any copper-zinc alloy which serves as 
anode, is composed, according to Hess, as follows : 

V. Sodium bicarbonate, 14f ozs., crystallized ammonium 
chloride 9| ozs., 98 per cent, potassium cyanide 1\ ozs., water 
10 quarts. 

Cast metal plates are to be used as anodes. Transfer begins 
after a current of medium strength has for a few hours passed 
through the bath. 

This bath is also well adapted for the deposition of tombac 
with the use of tombac anodes. Most suitable electro-motive 
force, 3 to 3.5 volts. 

Fresh brass baths work, as a rule, more irregularly than any 
other baths containing cyanide, the deposit being either too 
red or too green or gray, while frequently one side of the ob- 
ject is coated quite well, and the other not at all. To force 
the bath to work correctly it must be thoroughly boiled, the 
water which is lost by evaporation being replaced by the ad- 
dition of distilled water or pure rain water. If boiling is to 
be avoided, the bath, as previously mentioned, is worked 
through for hours, and even for days, with the current, until 
an object suspended in it is correctly brassed. 

Prepared brass salts. Regarding these salts, we refer to what 
has been said in reference to coppering salts, p. 332. For a 
100-quart brass bath, with 92.59 grains of brass, use 6.6 lbs. 
of double brass salt and 7 ozs. of 98 to 99 per cent, potassium 
cyanide, and for a 100-quart brass bath with 138.88 grains of 
brass per quart 9.9 lbs. of brass double salt and 7 ozs. of 98 to 
99 per cent, potassium cyanide. 

As for copper baths prepared with double salts, an addition 



DEPOSITION OF COPPER, BRASS AND BRONZE. 355 

of 80 to 46 grains of potassium cyanide per liter and of a suit- 
able conducting salt (neutral sodium sulphite) may be recom- 
mended. 

Tanks for brass baths. What has been said on this subject 
under tanks for copper cyanide baths (p. 335) applies also to 
brass baths. 

Brass anodes. Sheets of brass, annealed and pickled bright, 
not rolled too hard and of as nearly as possible the same com- 
position and color as the deposit is to have, are used as anodes. 

Cast anodes have the advantage of being more readily solu- 
ble, and therefore keep the content of metal in the bath more 
constant than rolled brass anodes. However, the latter answer 
very well if care is taken to from time to time increase 
the content of metal in the bath. The anode-surface in the 
bath should be as large as possible, since with slight anode 
current-densities the formation of slime on the anodes is less 
than when the contrary is the case. 

Execution of brassing. As previously mentioned, the color 
of the deposits depends on the quantitative proportions of the 
two metals deposited, a weaker current depositing predomi- 
nantly copper, and a stronger current more zinc. Hence by 
the use of a rheostat it is in the power of the operator to effect 
within the limits which are given by the resistances of the 
rheostat, deposits of brass alloys of a redder or more pale 
yellow to greenish color, according to whether the resistance 
is increased or decreased. 

However, according to the composition of the brass bath, 
and especially with baths which have for a long time been in 
use, a determined color of the alloy to be deposited cannot be 
produced with the assistance of the rheostat. In such case the 
content of metal in the bath which is required and lacking for 
the production of a determined color, must be augmented by 
the addition of solution of the respective metallic salts, or in 
the form of double salt. 

Suppose a bath which originally contained copper and zinc 
salts in equal proportions has been long in daily use. Now, 



356 ELECTRO-DEPOSITION OF METALS. 

since brass contains more copper than zinc the deposit will be 
richer in copper, and it is evident that more of the latter will 
be withdrawn from the bath than of zinc, and finally a limit 
will be reached when the bath with a current suitable for the 
decomposition of the solution will deposit a greenish or gray 
brass, and with a weaker current produce no deposit whatever. 
The only remedy in such a case is the addition of sufficient 
solution of copper cyanide in potassium cyanide, so that, even 
with quite a powerful current, a deposit of a beautiful brass 
color is produced, the shades of which can then again be con- 
trolled with the assistance of the rheostat. Instead of dissolv- 
ing copper cyanide in potassium cyanide, it is better to directly 
use crystallized potassium-copper cyanide. However, it must 
not be forgotten that every addition of a metallic salt momen- 
tarily irritates the brass bath, making it, so to say, sick, and to 
confine this feature to the narrowest limit, an addition of car- 
bonate and bisulphite of soda, or only of neutral bisulphite of 
soda, should at the same time be made, and the bath be 
worked through with the current as previously described, until 
a test shows that it works in a regular manner. The effect of 
the addition cannot be controlled in any other way, and more 
might be added than is required and desirable. If. however, 
the quantity of the addition is shown not to be sufficient, the 
operation is continued till the object is attained. 

As in the copper bath, an abundant formation of slime on 
the anodes indicates the want of potassium cyanide in the bath. 
In this case the evolution of gas-bubbles on the objects is very 
slight, and the deposit forms slowly. This is remedied by an 
addition of potassium cyanide. However, in brass baths con- 
taining the standard excess of free potassium cyanide, the for- 
mation of slime has also a disturbing effect, when the baths 
are for a longer time worked without interruption. The solu- 
tion by the potassium cyanide of the bathi of the metallic 
cyanides formed on the anodes takes place more slowly than 
their formation. If the operation of the bath is for some time 
interrupted, gradual solution takes place and the greater part 



DEPOSITION OF COPPER, BRASS AND BRONZE. 357 

of the slime on the anodes disappears. However, with an un- 
interrupted use of the bath, the layer of slime frequently in- 
creases to such an extent that the current cannot flow through 
the anodes into the bath. In such a case, the further increase 
of the content of potassium cyanide would not be advisable, 
since it would exceed the limit admissible for a dense deposit ; 
frequent mechanical cleaning of the anodes is then the best 
remedy. A particularly dense slime on the anodes is }'ielded 
by baths which contain small quantities of conducting salts, 
such, for instance, as are prepared from the double and triple 
salts. By giving such baths additions of sulphites or chlorides 
a less compact slime is formed which is favorable for solution 
in potassium cyanide. This effect is without doubt due to the 
anions of the conducting salts appearing on the anodes. 

The sluggish formation of the deposit, however, may also be 
due to a want of metallic salts. In this case not only potassium 
cyanide, but also solution of copper cyanide and zinc cyanide 
in potassium cyanide, has to be added. For this purpose pre- 
pare a concentrated solution of potassium cyanide in water, 
and a solution of equal parts of blue vitriol and zinc sulphate 
in water. From the latter, precipitate the copper and zinc as 
carbonates with a solution of carbonate of soda as given in 
formula I. After allowing the precipitate to settle, pour off 
the clear supernatant fluid, and add to the precipitate, stirring 
vigorously, of the potassium cyanide solution until it is dis- 
solved ; if heating takes place thereby, add from time to time 
a little cold water. Add this solution with a small excess of 
potassium cyanide, and the addition of carbonate or bisulphite 
of soda, to the bath, and boil the latter or work it through 
with the current. A more simple method is to procure cop- 
per cyanide and zinc cyanide, or concentrated solutions of 
these combinations, from a dealer in such articles. In the 
first case, rub in a mortar equal parts of zinc cyanide and 
copper cyanide with water to a thinly-fluid paste. Pour this 
paste into a potassium cyanide solution, containing about 7 
ozs. of potassium cyanide to the quart, as long as the metallic 



358 ELECTRO-DEPOSITION OF METALS. 

cyanides dissolve quite rapidly by stirring. When solution 
takes place but slowl} r , stop the addition of paste. A still 
more simple way is to buy crystallized potassium-copper cya- 
nide and potassium-zinc c} r anide, dissolve these salts in suit- 
able quantitative proportions, and add the solution to the 
bath. 

When a brass bath contains too great, an excess of potassium 
cyanide, a very vigorous evolution of gas takes place on the 
objects, but the deposit is formed slowly or not at all ; besides; 
the deposit formed has a tendency to peel off in scratch-brush- 
ing. In this case the injurious excess has to be removed, 
which is effected by pouring, whilst stirring vigorously, a 
quantity of the above-mentioned thinly-fluid paste of zinc 
cyanide and of copper cyanide into the bath. The addition 
of metallic cyanides is continued only so long as they dissolve 
with rapidity, so as not to fix all the free potassium cyanide 
of the bath. 

When a brass bath has not been used for some time a white 
film frequently forms on its surface. This is best removed by 
pushing it by means of a piece of twisted paper into one corner 
of the bath, and lifting it off with a shallow dish. It may 
then be dissolved, eventually by heating, in a small quantity 
of potassium cyanide and the solution added to the bath. 

To avoid unnecessary repetition we refer, as regards the 
production of thick deposits, scratch-brushing and polishing 
of the plated articles, to what has been said under " Execution 
of Coppering," the directions given there being also valid for 
brassing. 

The deposition of several metals from a common solution is 
not an easy task, and requires attention and experience. If, 
however, the directions given in this chapter are followed, the 
operator will be able to conduct, after short experience, the 
brassing process with the same success as one in which but one 
metal is deposited. 

Special attention must be paid to frequent thorough mixing 
of the contents of the bath, so that the fluids are renewed on 



DEPOSITION OF COPPER, BRASS AND BRONZE. 359 

the cathodes, because otherwise, by reason of the fluid becom- 
ing poor in metal, the deposit would show different composi- 
tions, and consequently other colors. 

For the production of deposits of brass which are to show a 
tone resembling gold, it has been recommended to add to the 
brass bath an aluminium salt, such as aluminium chloride, 
aluminium sulphate, etc. Such baths have been offered to lay- 
men as aluminium-bronze baths, with the assurance that the 
deposit obtained from them consists of an alloy of aluminium 
and brass, and possesses the same power of resisting atmospheric 
influences as aluminium-bronze. Although these commenda- 
tions are evidently misleading, because, notwithstanding, in- 
numerable receipts for the production of electro-deposits of 
aluminium, the reduction of this metal from solutions of its 
salts has thus far not been successfully accomplished. De- 
posits produced in such brass baths, compounded with alu- 
minium salts, were subjected to examination, and in no case 
was it possible to establish even the slightest trace of alu- 
minium in the deposit. However, notwithstanding that a 
reduction of aluminium does not take place, the influence of 
an addition of an aluminium salt to brass baths, as regards 
the result of the brass tone, cannot be denied, but up to the 
present time it has been impossible to find an explanation of 
this fact. If a brass bath, prepared according to the formulas 
given above, be compounded with 35 to 40 grains of alu- 
minium chloride per quart of bath, the resulting deposit 
shows a warmer, more sad brass tone than that yielded by a 
bath without such an addition, and if the bath is somewhat 
rich in copper, the color of the deposit almost resembles red 
gold. However, greater power of resisting atmospheric influ- 
ence could not be noticed, neither can such be expected, since 
the deposit consists solely of zinc and copper. 

It remains to be mentioned that in brassing, the distance of 
the objects to be plated from the anodes is of considerable 
importance. If objects with deep depressions or high reliefs 
are suspended in the brass bath, it will be found that, with the 



360 ELECTRO-DEPOSITION OF METALS. 

customary distance of 3f to 5f inches from the anodes, the 
brassing of the portions in relief nearest to the anodes will turn 
out a lighter color than that of the depressed portions, which 
will show a redder deposit, the reason for this being that the 
current acts more strongly upon the portions in relief, and con- 
sequently deposits more zinc than the weaker current which 
strikes the depressions. To equalize this difference the objects 
have to be correspondingly further removed from the anodes, 
with lamp-feet up to 9f inches, and even more, when a deposit 
of the same color will be everywhere formed. 

The brassing of unground iron castings is especially trouble- 
some, and in order to obtain a beautiful and clean deposit the 
preliminary scratch-brushing has to be executed with special 
care; but even then the color of the brass deposit will some- 
times be found to possess a disagreeable gray tone. This is 
very likely largely due to the quality of the iron itself, and it 
is advisable first to give the casting a thin coat of nickel or 
or tin, upon which a deposit of brass of the usual brilliancy 
can be produced. In baths serving for brassing iron articles, 
a large excess of potassium cyanide must be avoided. It is, 
however, an advantage to increase the content of carbonate of 
soda. 

Inlaying of brassed objects with black is done in the same 
manner as described under " Deposition of Copper." 

Brassing by contact will be referred to in the chapter " Depo- 
sitions by Contact." 

For oxidizing, patinizing and coloring of brass, see special 
chapter. 

Examination of brass baths. The characteristic indications 
by which a deficiency, and too large an excess of potassium 
cyanide in the bath, as well as an insufficient content of metal, 
may be recognized, have already been discussed, and it is here 
only necessary to refer to the quantitative determination of the 
separate constituents. 

Free potassium cyanide and the content of copper are deter- 
mined in the same manner as described under copper baths 



DEPOSITION OF COPPER, BRASS AND BRONZE. 361 

containing potassium cyanide. Hence only the determination 
of zinc has here to be considered. For making this deter- 
mination it is necessary to destroy the cyanide combinations, 
and entirely to remove the copper. For this purpose bring by 
means of the pipette 10 cubic centimeters of the brass bath 
into a porcelain dish, and proceed in the same manner as given 
on page 345 for the determination of copper by electrolysis. 
Dissolve the evaporated residue in the dish in water, adding 
a few drops of pure hydrochloric acid. Then bring the solu- 
tion into a capacious beaker, dilute with water to about 250 
cubic centimeters, and heat to boiling. Now add about 10 
cubic centimeters of pure dilute sulphuric acid (1 : 10) and 
stirring constantly, mix with a solution of 2.5 grammes of 
crystallized sodium. Copper sulphide is separated while the 
sulphurous acid escapes. Cover the beaker with a watch-glass, 
let it stand for 15 minutes, and then filter off the precipitate. 
Wash the filter thoroughly with sulphuretted hydrogen water, 
and evaporate the filtrate together with the wash waters to 
about 100 to 150 cubic centimeters. The solution contains all 
the zinc, and can be at once titrated (see below). 

For the determination of zinc by electrolysis, heat the solu- 
tion to boiling, mix it with solution of sodium carbonate in 
excess, and after the precipitate of basic zinc carbonate has 
settled, filter it off. Dissolve the precipitate in the filter with 
pure dilute sulphuric acid, bring the filtrate, together with the 
waters used for thoroughly washing the filter, into a clean 
beaker, and neutralize accurately with sodium carbonate. 

Now bring into the platinum dish, previously coppered, 5 
grammes of potassium oxalate and 2 grammes of potassium 
sulphate dissolved in a small quantity of water, fill the plati- 
num dish up to within 1 centimeter from the rim with distilled 
water, and electrolyze with a current-density of ND 100 = 0.5 
ampere. The dull, bluish-white deposit of zinc is treated with 
water, then with alcohol and ether, dried in the exsiccator 
over sulphuric acid and weighed. The determined weight of 
the zinc deposit multiplied by 100 gives the content of zinc in 
grammes per liter of brass bath. 



362 ELECTRO-DEPOSITION OF METALS. 

For the volumetric determination of the zinc, about 100 to 150 
cubic centimeters of the zinc solution resulting after the pre- 
cipitation of the copper are used. The determination is based 
upon the principle that potassium ferrocyanide solution pre- 
cipitates the zinc from the solution, and that complete precip- 
itation is indicated by an excess of potassium ferrocyanide, 
yielding a brown coloration with uranium acetate. If now the 
content of the potassium ferrocyanide solution is known, the 
quantity of it used gives the content of zinc. It is best to use 
a solution which contains per liter 32.45 grammes of pure 
crystallized potassium ferrocyanide, every cubic centimeter of 
this solution corresponding to 0.01 gramme of zinc. Add, 
stirring constantly, from a burette potassium ferrocyanide 
solution to the zinc solution in a beaker until a drop of the 
fluid brought upon a strip of filtering paper previously satu- 
rated with uranium acetate solution and again dried just 
shows the commencement of a brown coloration. 

Since 10 cubic centimeters of the brass bath were used for 
the determination, the number of cubic centimeters of potas- 
sium ferrocyanide solution consumed gives the quantity of 
zinc in grammes per liter of brass bath. Suppose 6 cubic 
centimeters of solution have been consumed, they would cor- 
respond to 0.06 gramme zinc (0.01 X 6). Hence since in 10 
cubic centimeters of bath 0.06 gramme of zinc is present, the 
bath contains 6 grammes (0.06 X 100) of zinc per liter. 

If thus a deficiency of zinc in the bath, due to long-continued 
working, has been determined the initial content can be readily 
restored by the addition of pure potassium zinc cyanide. The 
latter contains 26 per cent, of zinc, and the quantity required 
to be added is determined in the same manner as with a copper 
bath (see p. 348). 

Deposits of tombac, i. e., deposits having the color of tombac, 
ajre obtained by increasing the content of copper in the brass 
baths. 

The following formula gives a tombac bath which works 
well : 



DEPOSITION OF COPPER, BRASS AND BRONZE. 363 

Crystallized potassium copper cyanide 7 ozs., crystallized 
potassium-zinc cyanide 3| ozs., crystallized neutral bisulphite 
of soda 8| ozs., potassium cyanide f oz., water 10 quarts. 

Electro-motive force at 10 cm. electrode distance, 3 volts. 

Current-density. 0.3 ampere. 

It is of special advantage for the deposition of tombac to 
heat the bath to between 86° and 95° F., the resulting de- 
posits being of a more uniform color than at the ordinary 
temperature. 

For tombac deposits the transferring solution, according to 
Hess (see "Deposition of Brass," Formula V), may also be 
employed, tombac sheets being used as anodes. 

Deposits of bronze. Plating of metallic objects with bronze, 
i. e., a copper-tin alloy, or an alloy of copper, tin and zinc, is 
but seldom practiced, the bronze tone being in most cases 
imitated by a brass deposit with a somewhat larger content of 
copper. 

For coating wrought and cast-iron with bronze, Gountier 
recommends the following solution : 

Yellow prussiate of potash 10^ ozs., cuprous chloride 54; 
ozs., stannous chloride (tin salt) 14 ozs., sodium hyposulphite 
14 ozs., water 10 quarts. 

According to Ruolz. a bronze bath is prepared as follows : 
Dissolve at 122° to 140° F., copper cyanide 2.11 ozs., and 
oxide of tin 0.7 ozs., in 10 quarts of potassium cyanide solu- 
tion of 4° Be. The solution is to be filtered. 

Eisner prepares a bronze bath by dissolving 21 ozs. of blue 
vitriol in 10 quarts of water, and adding a solution of 2| ozs. 
of chloride of tin in potash lye. 

Salzede recommends the following bath, which is to be 
used at between 86° and 95° F. : Potassium cyanide 3| ozs., 
carbonate of potash 35| ozs., stannous chloride (tin salt) 0.42 
oz., cuprous chloride J oz., water 10 quarts. 

Weill and Newton claim to obtain beautiful bronze deposits 
from solutions of the double tartrate of copper and potash and 
the double tartrate of the protoxide of tin and potash, with 
caustic potash, but fail to state the proportions. 



364 ELECTRO-DEPOSITION OF METALS. 

The above formulae are here given with all reserve, since 
experiments with them failed to give satisfactory results. 
With Gountier's, Ruolz's and Eisner's baths no deposit was 
obtained, but only a strong evolution of hydrogen, while even 
with a strong current, Salzede's bath did not yield a bronze 
deposit, but simply one of tin. 

The following "method of preparing a bronze bath may be 
recommended : Prepare, each by itself, solutions of phosphate 
of copper and stannous chloride (tin salt) in sodium pyrophos- 
phate. From a blue vitriol solution precipitate, with sodium 
phosphate, phosphate of copper, allow the latter to settle, and 
after pouring off the clear supernatant fluid, bring it to solu- 
tion by concentrated solution of sodium pyrophosphate. On 
the other hand, add to a saturated solution of sodium pyro- 
phosphate, solution of tin sp.lt, as long as the milky precipi- 
tate formed dissolves. Of these two metallic solutions, add to 
a solution of sodium pyrophosphate, which contains about If 
ozs. of the salt to the quart, until the precipitate appears 
quickly and of the desired color. For anodes, use cast bronze 
plates, which dissolve well in the bath. Some sodium phos- 
phate has from time to time to be added to the bath, and if 
the color becomes too light, solution of copper, and if too 
dark, solution of tin. 

For nickel-bronze, see p. 315. 



CHAPTER VII. 



DEPOSITION OF SILVER. 



Silver (Ag = 107.88 parts by weight) and its properties. — 
Pure silver is the whitest of all known metals. It takes a fine 
polish, is softer and less tenacious than copper, but harder and 
more tenacious than gold. It is very malleable and ductile, 
and can be made into exceedingly thin leaves and fine wire. 
Its specific gravity is 10.48 to 10.55, according to whether it is 
cast or hammered. It melts at about 1832° F. It is unacted 
upon by the air, but in the atmosphere of towns it gradually 
becomes coated with a film of silver sulphide. It is rapidly 
dissolved by nitric acid, nitrogen dioxide being evolved. 
Hydrochloric acid has but little action upon it even at a boil- 
ing heat ; when heated with concentrated sulphuric acid it 
yields sulphur dioxide and silver sulphate. 

Chlorine acts upon silver at the ordinary temperature. 
Silver has great affinity for sulphur, and readily fuses with it 
to silver sulphide. Sulphuretted hydrogen blackens silver, 
brown-black silver sulphide being formed (tarnishing of silver 
in rooms in which gas is burned). Such tarnishing is most 
readily removed by potassium cyanide solution. 

Concentrated sulphuric acid combines at a boiling point with 
silver to silver sulphate, sulphurous acid escaping. Nitric acid 
readily dissolves silver at a gentle heat, and at a higher tem- 
perature with considerable violence, silver nitrate (lunar caus- 
tic) being formed, while nitrogen dioxide escapes. Watery 
chromic acid converts silver into red silver chromate, and this 
conversion is made use of as a test for silvering. By touch- 
ing silver or genuine silver-plating with a drop of a solution 
obtained by dissolving potassium dichromate in nitric acid of 
1.2 specific gravity, a red stain is formed. 

(365) 



3G6 ELECTRO-DEPOSITION OF METALS. 

Electro-plating with silver was, of all electro-metallurgical 
processes, the first which was carried on on a large scale and 
has reached enormous proportions. Large quantities of silver 
are annually consumed for this purpose, and it is to be re- 
gretted that no accurate statistics regarding this consumption 
are available. 

Silver baths. The longer an electro-plating process has been 
carried on, the greater, as a rule, the number of existing for- 
mulas for baths will be; but silver baths are an exception to this 
rule. If it is taken into consideration that silver-plating has 
been practically carried on for more than seventy years, the 
number of formulas might be expected to be at least equal to 
those for nickel-plating, which is of much more recent origin. 
Such, however, is not the case, and chiefly for the reason that 
the attempts to improve the silver baths, which were made 
either with a view to banish the poisonous potassium cyanide 
from the silver-plating industry, or otherwise to advance the 
plating process, could absolutely show no better results than 
the baths used by the first silver-platers. However, that 
attempts to make such improvements have not been entirely 
abandoned is shown by Zinin's proposition to substitute solu- 
tion of silver iodide in potassium iodide for a solution contain- 
ing potassium cyanide, or by Jordis' proposition to use silver 
lactate baths. While the bath according to Zinin yields bad 
results as compared with the old baths containing potassium 
cyanide, quite good silvering is obtained with a bath accord- 
ing to Jordis, but independent of the fact that the bath con- 
tains no potassium cyanide, no special advantages could be 
established. Hence there is no good reason for including 
other directions for silver baths in this work, which is pri- 
marily intended for practical use, and only formulas for the 
most approved baths will be given. 

However, before describing the preparation of the baths, a 
few words may be said in regard to the old dispute, whether it 
is preferable to use silver cyanide or silver chloride. Without 
touching upon all the arguments advanced, it may be asserted, 



DEPOSITION OF SILVER. 36T 

by reason of conscientious comparative experiments, that the 
results are the same, and that the life of the bath is also the 
same, whether one or the other salt has been used in its 
orginal preparation. From the chemical view-point, pre- 
ference had to be given to silver cyanide, but in practice, 
baths prepared with silver chloride were found to possess 
certain advantages, and theory has furnished an explanation 
of them. 

One of these advantages is found in the fact that by reason' 
of the potassium chloride formed, the resistance of a bath 
prepared with silver chloride is considerably less than that of" 
a silver cyanide bath, and, with the same current-density, the 
latter, therefore, requires a greater electro-motive force. 

Theoretically, preference has further to be given to silver 
chloride, because a portion of the potassium chloride formed' 
is dissociated, and potassium-ions and chlorine-ions thus get 
into the solution. These potassium-ions augment the potas- 
sium-ions which are present as a result of the dissociation of 
the potassium cyanide and silver cyanide and thus increase 
the efficiency. On the other hand, in addition to cyanogen- 
ions, chlorine-ions are separated on the anodes and augment 
the supply of silver-ions in the electrolytes. Furthermore, the 
presence of potassium chloride facilitates the conversion of the 
silver cyanide formed on the anodes into potassium silver 
cyanide, according to the following equation : 

2AgCy + KC1 = KA g Cy 2 + AgCl 

Silver cyanide. Potassium chloride. Potassium silver Silver chloride. 

cyanide. 

While, according to this, preference may be given to silver 
chloride for the preparation of silver baths, and the more so as 
it is more easily prepared than silver cyanide, yet for refresh- 
ing the baths, which becomes from time to time necessary to 
increase their content of silver, recourse must be had to silver 
cyanide, because with the use of silver chloride for this pur- 
pose, the baths would become thick in consequence of a con- 



368 ELECTRO-DEPOSITION OF METALS. 

stant supply of further quantities of potassium chloride, and 
the silver separate with a coarse structure. 

Silver-bath for a heavy deposit of silver (silvering by weight). 

I. 98 to 99 per cent, potassium cyanide 14 ozs., fine silver 
as silver chloride 8f ozs., distilled water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 0.75 volt. 

Current density, 0.3 ampere. 

la. 98 to 99 per cent, potassium cyanide 8| ozs., fine silver 
as silver cyanide "8f ozs., distilled water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 1 volt. 

Current density, 0.3 ampere. 

Preparation of bath 1. with silver chloride. Dissolve 14 ozs. 
of chemically pure nitrate of silver, best the crystallized, and 
not the fused article, in 5 quarts of water, and add to the 
solution pure hydrochloric acid, or common salt solution, with 
vigorous stirring or shaking, until a sample of the fluid filtered 
through a paper filter forms no longer a white caseous pre- 
cipitate of silver chloride when compounded with a drop of 
hydrochloric acid. These, as well as the succeeding opera- 
tions, until the silver chloride is ready, have to be performed 
in a darkened room, as silver chloride is partially decomposed 
by light. Now separate the precipitate of silver chloride from 
the solution by filtering, using best a large bag of close felt, 
and wash the precipitate in the felt bag with fresh water. 
Continue the washing until blue litmus paper is no longer 
reddened by the wash-water, if hydrochloric acid was used 
for precipitating, or, if common salt solution was used, until 
a small quantity of the wash-water, on being mixed with a 
drop of lunar caustic solution, produces only a slight milky 
turbidity and no precipitate. Now bring the washed silver 
chloride in portions from the felt bag into a porcelain mortar, 
rub it with water to a thin paste, and pour the latter into the 
potassium cyanide solution consisting of 14 ozs. of 98 per 
cent, potassium cyanide in 5 quarts of water, in which, by 
vigorous stirring, the silver chloride gradually dissolves. All 
the precipitated silver chloride having been brought into 



DEPOSITION OF SILVER. 369 

solution, dilute with water to 10 quarts of fluid, and boil the 
bath, if possible, for an hour, replacing the water lost by 
■evaporation. A small quantity of black sediment containing 
silver thereby separates, from which the colorless fluid is 
filtered off. This sediment is added to the silver residues, 
and is worked together with them for the recovery of the 
silver by one of the methods to be described later on. 

Preparation of bath la with silver cyanide. Dissolve 14 
ounces of chemically pure crystallized nitrate of silver in 5 
quarts of water, and precipitate the silver with prussic acid, 
adding the latter until no more precipitate is produced by the 
addition of a few drops of prussic acid to a filtered sample of 
the fluid. Now r filter, wash, and proceed for the rest exactly 
as stated for the bath with silver chloride, except that only 8f 
ounces of potassium cyanide are taken for dissolving the silver 
■cyanide. In working w T ith prussic acid avoid inhaling the 
vapor which escapes from the liquid prussic acid, especially 
in the warm season of the year ; and be careful the acid does 
not come in contact with cuts on the hands. It is one of the 
most rapidl} r acting poisons. 

Silver cyanide may also be prepared as follows : Dissolve 
14 ounces of chemically pure crystallized nitrate of silver in 5 
quarts of water, and add moderately concentrated potassium 
cyanide solution until no more precipitate is formed, avoid- 
ing, however, an excess of the precipitating agent, as it would 
again dissolve a portion of the silver cyanide. The precipi- 
tated silver cyanide is filtered off, washed and dissolved in 
potassium cyanide, as above described. 

The preparation of the silver bath according to the above 
formulas is more conveniently effected by using pure crystal- 
lized potassium-silver nitrate in the following proportions : 

16. 98-per cent, potassium cyanide, 6^ to 7 ozs. ; crystal- 
lized potassium-silver cyanide, 17| ozs. ; distilled water, 10 
quarts. 

Electro-motive force aud current-density as for la. 

The salts are simply dissolved in the cold water. 
24 



370 ELECTRO-DEPOSITION OF METALS. 

The baths prepared according to formulas I, la or lb serve- 
chiefly for the production of a heavy deposit upon German 
silver articles, especially table and other household utensils. 
Of course, they may also be used for plating other metals by 
weight. 

Silver bath for ordinary electro-silvering. II. 98-per cent, 
potassium cyanide, 6f to 7 ounces ; fine silver (as silver 
nitrate or chloride), 3 J ounces ; distilled water, 10 quarts. 

Electro-motive force, for silver chloride, at 10 cm. electrode- 
distance, 1.25 volts. 

Current-density, 0.3 ampere. 

To prepare the bath dissolve 5| ounces of chemically pure 
crystallized nitrate of silver in 5 quarts of distilled water ; in 
the other 5 quarts of water dissolve the potassium cyanide, and 
mix both solutions. Or if chloride of silver is to be used, pre- 
cipitate the solution of 3| ounces of the silver salt in the same 
manner as given for formula I ; wash the precipitated chloride 
of silver, and dissolve it in the potassium cyanide solution. 

Ila. 98-per cent, potassium cyanide If ozs., crystallized 
potassium-silver cyanide 7 ozs,, distilled water 10 quarts. 

Dissolve the salts in the cold water. 

For the preparation of silver baths double and triple silver 
salts are brought into commerce by some manufacturers. 

Such salts require simply dissolving in water. However,, 
they offer no special advantages, since the preparation of baths- 
according to formulas 16 and Ila can scarcely be surpassed as- 
regards simplicity. 

Tanks for silver baths. As receptacles for silver baths, tanks- 
of stoneware and enameled iron tanks, as well as wood tanks- 
lead-lined and coated or lined with celluloid can only be used. 

Treatment of the silver baths. — Silver anodes. Frequently the 
error is committed of adding too much potassium cyanide 
to the bath. A certain excess of it must be present, and in 
the formulas given, this has been taken into consideration. 
For dissolving the silver cyanide prepared from 14 ounces of 
nitrate of silver, as given in formula la, only about 5J ounces- 



DEPOSITION OP SILVER. 371 

of potassium cyanide are required, and the consequence of 
working with such a bath, devoid of all excess, would be that, 
on the one hand, the bath would offer considerable resistance 
to the current, and, on the other, that the deposit would not 
be uniform and homogeneous, and the anodes would be coated 
with silver cyanide. Hence, with the use of a normal current, 
about 0.35 to 0.42 oz. more of potassium cyanide is added 
per quart of bath. However, when working with a stronger 
current, this excess would already be too large, and the 
deposit would not adhere properly, and rise up in scratch- 
brushing. And, again, with a very weak current, the baths 
can without disadvantage stand a larger excess. As a rule, 
however, the proportions between fine silver and potassium 
cyanide given in the above formulae may be considered as 
normal, and with the current-densities prescribed, a deposit 
of fine structure, which adheres firmly, will result. 

By reason of the slight electro-motive force required for 
silvering, in plating larger object-surfaces the cells are not 
coupled one after the other for electro-motive force, but in 
parallel. In no case must an evolution of hydrogen be per- 
ceptible on the objects, and the current must be the more 
weakened, the larger the excess of potassium cyanide in the 
bath. 

In the silver baths prepared according to the formulas given 
above, the excess of potassium cyanide amounts to 0.35 to 
0.42 oz. per quart, and is only increased in silver baths which 
are to serve for the direct silvering of tin and of alloys with a 
large content of nickel, as will be shown later on. Baths for 
ordinary, as well as light, silvering, with 0.35 oz. of silver per 
quart, would only require an excess of 0.17 oz. of potassium 
cyanide. However, since the larger excess of 0.35 oz. is no 
disadvantage, and allows of working with less electro-motive 
force, it is generally preferred. The electro-motive force given 
for the separate formulas is applicable only when the anode- 
surface is of the same size, or approximately so, as the object- 
surface. If, for reasons of economy, the work is carried on 



372 ELECTRO-DEPOSTTION OF METALS. 

with considerably smaller anode-surfaces, the electro-motive 
force has to be adequately increased in order to conduct into 
the bath a quantity of current corresponding to the normal 
current-density. 

Whether too much, or not enough, potassium cyanide is 
present in the bath is indicated by the appearance of the 
plated objects and the properties of the deposit, as well as by 
the behavior of the anodes in the bath during and after silver- 
ing. It may be accepted, as a rule, that with a moderate 
current the object should, in the course of 10 to 15 minutes, 
be coated with a thin, dead-white film of silver. If this be 
not the case, and the film of silver shows a meager bluish- 
white tone, potassium cyanide is wanting. However, if, on 
the other hand, the dead-white deposit forms within 2 or 3 
minutes, and shows a crystalline structure, or a dark tone 
playing into gray-black, the content of potassium cyanide in 
the bath is too large, provided the current is not excessively 
strong. If copper and brass become coated with silver with- 
out the co-operation of the current, the bath contains too 
much potassium cyanide. 

In silver-plating, even if the objects are to be only thinly 
coated, insoluble platinum anodes should never be used, but 
only anodes of fine silver, which are capable of maintaining 
the content of silver in the bath quite constant. From the 
behavior and appearance of the anodes, a conclusion may also 
be drawn as to whether the content of potassium cyanide in 
the bath is too large or too small. If the anodes remain 
silver- white during plating, it is a sure sign that the bath 
contains more potassium cyanide than is necessary and de- 
sirable ; but. if they turn gray or blackish, and retain this 
color after plating, when no current is introduced into the 
bath for a quarter of an hour or more, potassium cyanide is 
wanting. On the other hand, the correct content of potassium 
cyanide is present, when the anodes acquire during the plat- 
ing process a gray tone, which, after the interruption of the 
current, gradually changes back to pure white. 



DEPOSITION OF SILVER. 373 

The use of steel sheets as anodes for silver baths in place of 
silver anodes, as has been proposed, cannot be approved, 
especially when chloride of silver has been used for the 
preparation of the bath, or other chlorides are present in 
it. The chloride-ions would bring iron into solution and 
this would form potassium-ferrocyanide with the potassium 
cyanide. , 

If it is shown by the process of silvering itself, or by the 
appearance of the articles, or of the anodes, that potassium cya- 
nide is wanting in the bath, it should be immediately added, 
though never more than 30 to 37| grains per quart of bath at 
one time, so as to avoid going to the other extreme. Too large 
a content of potassium cyanide is remedied by adding to the 
bath, stirring constantly, a small quantity of cyanide or chlo- 
ride of silver rubbed with water to a thinly-fluid paste, whereby 
the excess is rendered harmless in consequence of the formation 
of the double salt of silver and potassium cyanide. Instead of 
such addition, the current, may, however, be used for correct- 
ing the excess. For this purpose suspend as many silver 
anodes as possible to the anode-fods, but only a single anode 
as an object to the object-rod, and allow the current to pass 
for a few hours through the bath, whereby the excess of 
potassium cyanide is removed or rendered harmless by the 
dissolving silver. 

The bath can be kept quite constant by silver anodes, pro- 
vided potassium cyanide be regularly added at certain inter- 
vals, and the anode-surface is equal to that of the objects to 
be plated. But since, on account of the expense, a relatively 
small anode-surface is frequently used, the content of silver in 
a bath continuously worked will finally become lower, and 
augmentation, by the addition of silver, will be required. The 
manner of effecting this augmentation depends on whether the 
baths are used for plating by weight or for lighter silvering, or 
whether the baths are worked without stopping from morning 
till evening. For replacing the deficiency in baths prepared 
according to formulae I and la, it is advisable to use exclu- 



374 ELECTRO-DEPOSITION OF METALS. 

sively solution of silver cyanide in potassium cyanide, or of 
crystallized potassium-silver cyanide in water. 

It has previously been mentioned that with proper treatment 
baths made with chloride of silver have the same duration of 
life as those prepared with silver cyanide. The chief feature 
of such proper treatment is not to use chloride of silver dis- 
solved in potassium cyanide foe augmenting the content of 
silver, but to employ silver cyanide instead, since by the use of 
the former, the bath thickens in consequence of the potassium 
chloride which is simultaneously introduced. The effect of 
such thickening is that the deposits are formed less homo- 
geneously and with coarser structure. 

A gradual thickening of the bath may also take place if po- 
tassium cyanide containing potash is used, instead of the prep- 
aration free from potash, and of 98 to 99 per cent, purity. Even 
pure fused potassium cyanide produces a thickening of the 
bath, which, however, progresses very slowly. This thicken- 
ing is due to a portion of the excess of potassium cyanide being 
by the action of the air converted into potassium carbonate, 
and if the quantity of the latter exceeds £ oz. per quart, it has 
to be neutralized. For this purpose prussic acid was formerly 
used in order to effect a conversion of the potassium carbonate 
into potassium cyanide. It is, however, a well-known fact 
that carbonic acid decomposes the potassium cyanide, potas- 
sium carbonate and prussic acid being formed, and the addi- 
tion of prussic acid would therefore appear not very suitable 
for attaining the object in view. 

It is better to use solutions of calcium cyanide or barium 
cyanide, and add them so long as a precij)itate of calcium car- 
bonate or barium carbonate is formed. The solutions should, 
however, be freshly prepared. The precipitate formed is 
allowed to settle when the clear solution is siphoned off, and 
the residue filtered through a paper filter. 

Since, as mentioned above, the proportion of excess of potas- 
sium cyanide to the content of silver undergoes changes ac- 
cording to the proportion of the object-surface to the anode- 



DEPOSITION OP SILVER. 375 

surface, the temperature of the bath, etc., it becomes necessary 
to add one or the other in order to maintain the proper pro- 
portions and the effective working of the bath. 

To determine rapidly whether the bath contains silver and 
excess of potassium cyanide in proper proportions, the follow- 
ing methods may be used: Dissolve 1 gramme (15.43 grains) 
of chemically pure crystallized nitrate of silver in 20 grammes 
,(0.7 oz.) of water and gradually add this solution, whilst con- 
stantly stirring with a glass rod, to 100 grammes (3.52 ozs.) 
of the silver bath in a beaker, so long as the precipitate of 
silver cyanide formed dissolves by itself. If, after adding the 
entire quantity of silver solution, the precipitate dissolves rap- 
idly, too large an excess of potassium cyanide is present in the 
bath ; and vice versa, if the precipitate does not completely 
•dissolve, after stirring, potassium cyanide is wanting. 

The quantitative determination of the content of potassium 
-cyanide and of silver will be described later on under " Ex- 
amination of Silver Baths." 

Agitation of silver baths. In heavy silver-plating, constant 
agitation of the strata of fluid is of decided advantage, grooves 
and blooms being otherwise readily formed upon the plated 
■objects, especially when the baths are over-concentrated or 
thickened. The depressed grooves can only be explained by 
the fact that the strata of fluid on the cathodes having become 
-specifically lighter by yielding metal are subject to a current 
towards the surface ; the lower strata richer in silver give rise 
to heavier deposits on the lower cathode portions, so that 
■agitation of the bath becomes an actual necessity. 

With a bath in constant agitation a greater current-density 
may be used, the deposits, notwithstanding the greater current- 
density, forming with finer structure and in a correspondingly 
shorter time, which is especially noteworthy for heavy silver- 
ing. To keep the articles in gentle motion while in the bath, 
one method is to connect the suspending rods to a frame of 
iron having four wheels, about 3 inches in diameter, connected 
to it, which slowly travel to and fro to the extent of 3 or 4 



376 



ELECTRO-DEPOSITION OF METALS. 



inches upon inclined rails attached to the upper edge of tho 
tank, the motion, which is both horizontal and vertical, being 
given by means of an eccentric wheel driven by steam power. 
By another arrangement, the frame supporting the articles 
does not rest upon the tank, but is suspended above the bath, 
and receives a slow swinging motion from a small eccentric or 
its equivalent. In the Elkington establishment at Birming- 
ham the following arrangement is in use : All the suspending 
rods of the bath rest upon a copper mounting, which, b} r each 
revolution of an eccentric wheel, is lifted about f inch, and 
then returned to its position. The copper mounting is con- 

Fig. 123. 




nected to the main negative wire of the dynamo-machine by 
a copper cable. The same object may also be attained by giv- 
ing the articles a horizontal, instead of a vertical motion, as- 
shown in Fig. 123, in which the motion is produced by an 
eccentric ^heel on the side. 

With equal, if not better, success the mechanically moved 
stirring apparatus, which will be described under " Copper 
Galvanoplasty," may be used. In this apparatus several glass 
rods movable around a pivot keep the bath in constant motion. 
Where such a stirring apparatus cannot be conveniently 



DEPOSITION OP SILVER. 377' 

arranged, the motion of the bath may be produced by intro- 
ducing, by means of a pump, air on the bottom of the tank. 

A singular phenomenon in regard to silver baths, which 
has not yet been explained, may here be mentioned. A small 
addition of certain, and especially of organic, substances, 
which, however, must not be made suddenly or in too large 
quantities, produces a fuller and better adhering deposit of 
greater luster than can be produced in fresh baths. Elking- 
ton observed that an addition of a few drops of carbon disul- 
phide to the bath made the silvering move lustrous, while 
others claim to have used with success solutions of iodine in 
chloroform, of gutta-percha in chloroform, as well as heavy 
hydrocarbons, tar, oils, etc. 

A silver bath, as shown by experience, becomes without 
doubt better in the degree in which it takes up small quan- 
tities of organic substances from the air and from dust; but 
numerous experiments have failed to confirm Elkington's 
observation that the formation of the deposit or its appearance 
is essentially influenced by the addition of carbon disulphide 
or any of the above-mentioned solutions of organic origin 
either in very small or considerable quantities. Many baths 
have been entirely spoiled by an attempt to change them into 
bright-working baths by the addition of such ingredients, and 
hence it is best to leave such experiments alone. It may, 
however, be stated that by the addition of a few drops of liquid 
ammonia, fresh silver baths accommodate themselves more 
rapidly to regular performance. 

However, the use of carbon disulphide as an addition to 
the silver bath for bright plating is advocated by some electro- 
platers, and some preparations for this purpose may here be 
given. The carbon disulphide should not be directly added 
to the bath, as in that case it does not intimately mix with 
the bath, it settling on the bottom of the vat and the deposit 
would turn out defective. The following plan has been highly 
recommended for the ordinary silver bath prepared from chlo- 
ride of silver and potassium cyanide : Add to 1 quart of the- 



378 ELECTRO-DEPOSITION OF METALS. 

silver bath in a bottle 10 drops of carbon disulpbicle. Cork 
tbe bottle tightly and vigorously shake from time to time. 
Allow the bottle to stand over night for the fluid to settle, and 
then pour off the supernatant fluid. A residue of a dark color 
will be found on the bottom of the bottle. The fluid thus 
obtained should be perfectly clear, and forms the carbon disul- 
phide solution to be added to the actual silver bath. 

For the preparation of a bath for bright-plating add about 
\ oz. of the carbon disulphide solution to every 45 quarts of 
the silver bath, and mix thoroughly. With proper treatment 
the deposit will be smooth and bright. 

If the deposit does not show the desired surface but is still 
partly mat and partly white, the bath does not contain suffi- 
cient carbon disulphide solution and more has to be added to 
obtain satisfactory results. Since the carbon disulphide is 
consumed in plating, carbon disulphide solution has of course 
to be added from time to time to the silver bath. The want 
of carbon disulphide in the bath is readily recognized by the 
appearance of the deposit. Care must, however, be exercised 
in making such an addition since too much of it has an 
injurious effect upon the deposit. The deposit thus obtained 
is smooth and has a slight luster. It is considerably harder 
than a mat deposit but can be polished without trouble. 

Another method of preparing a solution for bright-plating is 
as follows: Put 1 quart of ordinary silver-plating solution into 
a large stoppered bottle. Now add 1 pint of strong solution 
of cyanide, and shake well ; 4 ozs. of carbon disulphide are 
then added, as also 2 or 3 ozs. of liquid ammonia, and the 
bottle again well shaken, the latter operation being repeated 
every two or three hours. The solution is then set aside for 
about 24 hours, when it will be ready for use. About 2 ozs. 
of the clear liquid may be added to every 20 gallons of plating 
solution, and well mixed by stirring. A small quantity of the 
brightening solution may be added to the bath every day, and 
the liquid then gently stirred. In course of time the disulphide 
solution acquires a black color; to modify this a quantity of 



DEPOSITION OF SILVPJR. 379 

strong cyanide solution, equal to the brightening liquor which 
has been removed from the bottle, should be added each time. 
In adding the disulphide solution to the plating bath, an ex- 
cess must be avoided, otherwise the latter will be spoiled. 
Small doses repeated at intervals is the safer procedure, and 
less risky than the application of larger quantities, which may 
■ruin the bath. 

A very simple way to prepare the brightening solution is 
to put 2 or 3 ozs. of carbon disulphide into a bottle which 
holds rather more than half a gallon. Add to this about 3 
pints of old silver solution and shake the bottle well for a 
minute or so. Then nearly fill the bottle with a strong solu- 
tion of cyanide, shake well as before, and set aside for at least 
24 hours. Add about 2 ozs. (not more) of the brightening 
liquor, without shaking the bottle, to each 20 gallons of solu- 
tion in the plating vat. Even at the risk of a little loss from 
•evaporation, it is best to add the brightening liquor to the 
bath the last thing in the evening, when the solution should 
be well stirred so as to thoroughly diffuse the added liquor. 
The night's repose will leave the bath in good working order 
for the following morning. 

Yellow tone of silvering. After plating, the objects fre- 
quently show, instead of a pure white, a yellow tone, or they 
become yellow in the air, which is ascribed to the formation of 
basic silver salts in the deposit. To overcome this evil it has 
been proposed to allow the objects to remain in the bath for a 
few minutes after interrupting the current, whereby the basic 
salts are dissolved by the potassium cyanide of the bath ; or 
the same object is attained by inverting the electrodes for a 
few seconds, after plating, thus transforming the articles into 
anodes. The electric current carries away the basic salt of 
silver in preference to the metal. This operation should, of 
course, not be prolonged, otherwise the silver will be entirely 
removed from the objects, and will be deposited on the anodes. 
For the same purpose some electro-platers hold in readiness a 
warm solution of potassium cyanide, in which they immerse 
the plated articles for half a minute. 



380 ELECTRO-DEPOSITION OF METALS. 

Silver alloys. It has been proposed to add to the silver 
baths a solution of nickelous cyanide in potassium cyanide in 
order to obtain a deposit of a silver-nickel alloy, which is 
claimed to be distinguished by its greater hardness and the 
property of not so readily turning dark. Numerous experi- 
ments with solutions of cyanide of silver and nickelous cyanide 
in potassium cyanide in all possible proportions, and with 
various electro-motive forces, and subsequent analysis of the 
deposits obtained, showed, however, only inconsiderable traces 
of nickel in the silver deposit, which had but a very slight 
influence upon the hardness and durability of the silver. 

The London Metallurgical Co. endeavors to attain greater 
hardness and power of resistance of the silver by adding zinc 
cyanide or cadmium cyanide, and has given to this process 
the name of areas silver-plating. According to the patent, an 
addition of 20 to 30 per cent, of zinc or cadmium to the silver 
prevents the tarnishing of the plating, and besides the deposit 
is claimed to be lustrous and hard. For areas silver-plating 
the appropriate quantity of zinc or cadmium, or a mixture of 
both metals, is converted into potassium-zinc cyanide or 
potassium-cadmium cyanide, and this solution is mixed with 
a corresponding quantity of solution of potassium-silver cya- 
nide, with a small excess of potassium cyanide. Sheets of a 
silver-zinc or a silver-cadmium alloy are used as anodes. 

This method has been favorably commented upon by 
Sprague, Urquart and others, and some English platers claim 
that for many articles, especially bicycle parts, areas silvering 
may be substituted for nickeling. However these favorable 
opinions were not confirmed by the following experiments 
made by Dr. Langbein regarding the value of this process as a 
substitute for silver-plating instruments and articles of luxury. 

A bath w 7 as prepared which contained per quart 231^ troy 
grains of fine silver and 77 troy grains cadmium in the form 
of cyanide double salts with a small excess of potassium cya- 
nide. The most suitable tension of current for the decompo- 
sition of a pure potassium-cadmium cyanide solution which 



DEPOSITION OF SILVER. 381 

•contained per quart 154 troy grains of cadmium with the same 
excess of potassium cyanide as the above-mentioned mixture 
was found to be 2 volts. 

In electrolyzing the cadmium-silver bath with 0.75 volt, a 
uniform silver-white deposit similar to that of pure silver was 
at first formed. However, after two hours the deeper places 
of the objects suspended in the bath showed crystalline excres- 
cences which felt sandy, and could be rubbed off with the 
fingers. After scratch-brushing the articles and again sus- 
pending them in the bath, these sandy, non-adhering metallic 
deposits were rapidly reformed. An analysis of the deposit 
separated from the articles showed 96.4 per cent, silver and 
3.2 per cent, cadmium. This deposit could, without difficult}^, 
be polished with the steel like a pure silver deposit, and hence 
its hardness would not seem greater than that of pure silver. 
Its capability of resisting hydrogen sulphide as compared with 
pure silver was scarcely greater. 

In another experiment electrolysis was effected with 1.25 
volts. The deposit showed from the start a coarser structure, 
and the formation of the sandy non-adhering deposit took 
place much more rapidly. But, on the other hand, the hard- 
ness of the reduced coherent metal was greater than that of 
pure silver, and also its power of resisting hydrogen sulphide. 
An analysis of the deposit showed 92.1 per cent, silver and 
7.8 per cent, cadmium. In, both cases the deposit was dull 
like that of pure silver. 

With a greater electro-motive force the quantity of cad- 
mium in the deposit increased, and the hardness of the latter 
became correspondingly greater. However, these deposits 
could not be considered serviceable for the above-mentioned 
purpose, because they could not be made of sufficient thick- 
ness as required for solid silver-plating of forks and spoons. 

In Dr. Langbein's opinion, the decomposition-pressures of a 
solution of potassium-silver cyanide and of one of potassium- 
cadmium cyanide lie too far apart to obtain without dela}*- 
deposits of even composition and of sufficient density and 
Tthickness. 



382 ELECTRO-DEPOSITION OF METALS. 

Execution of silver-plating — A. Silver-plating by weight. — 
Copper, brass, and all other copper alloys may be directly 
plated after amalgamating (quicking), whilst iron, steel, nickel, 
zinc, tin, lead, and Britannia are first coppered or brassed, and 
then amalgamated. 

The mechanical and chemical preparation of the objects for 
the silver-plating process is the same as described on page 188 
et seq. To obtain well-adhering deposits great care must be 
exercised in freeing the objects from grease, and in pickling. 
As a rule, objects to be silver-plated are ground and polished. 
However, polishing must not be carried too far, since the de- 
posit of silver does not adhere well to highly polished surfaces; 
and in case such highly polished objects are to be silvered it 
is best to deprive them of their smoothness by rubbing with 
pumice powder, emery, etc., or by pickling. 

The treatment of copper and its alloys, German silver and 
brass, which have chiefly to be considered in plating by 
weight is, therefore, as follows : 

1. Freeing from grease by hot potash or soda lye (1 part of 
caustic alkali to 8 to 10 parts of water), or by brushing with 
the lime-paste mentioned on page 229. 

2. Pickling in a mixture of 1 part, by weight, of sulphuric 
acid of 66° Be. and 10 of water. This pickling is only 
required for rough surfaces of castings, ground articles being 
immediately after freeing from grease treated according to 3. 

3. Rubbing with a piece of cloth dipped in fine pumice- 
powder or emery, after which the powder is to be removed by 
w r ashing. 

4. Pickling in the preliminary pickle, rinsing in hot water,. 
and quickly drawing through the bright-dipping bath (page 
223), and again thoroughly rinsing in several waters. 

5. Amalgamating (quicking) by immersion in a solution of 
mercury, called the quicking solution. This consists of a solu- 
tion of 0.35 ounce of nitrate of mercury in 1 quart of water, 
to which, while constantly stirring, pure nitric acid in small 
portions is added until a clear fluid results. A weak solution 



DEPOSITION OP SILVER. 383- 

of potassium-mercury cyanide in water is, however, to be pre- 
ferred, because the acid quickiug solution mentioned above 
makes the metals brittle. A quicking solution for silver- 
plating by weight consists of: Potassium-mercury cyanide, 14 
drachms to 1 oz. ; 99-per cent, potassium cyanide, 14 drachms; 
water, 1 quart. Care must be taken to bring the quicked 
objects into the bath as rapidly as possible, otherwise thin 
objects are liable to become brittle. The amalgam formed 
upon the surface penetrates to the interior of thin sheets if 
this action is not prevented by an immediate deposition of 
silver and the formation of silver amalgam. In the quicking 
solution the objects remain only long enough to acquire a 
uniform white coating, when — 

6. They are rinsed in clean water, and gone over with a 
soft brush in case the quicking shows a gray instead of a 
white tone. 

The articles are now brought into the silver bath, and: 
secured to the object-rods by slinging wires of pure 

Kto 1 24 

copper or, still better, of pure silver. The latter 
have the advantage that when by reason of a de- 
posit of considerable thickness having been formed 
upon them they have become useless for suspend- 
ing the articles, they can be directly converted into 
silver nitrate by dissolving in nitric acid, and used 
for the preparation of fresh baths, or for strengthen- 
ing old baths. 

When certain objects, for instance, forks and 
spoons, are to be plated, copper wires may be bent in the man- 
ner shown in Fig. 124. To prevent the deposition of silver 
upon the portions of the wire which do not serve for the pur- 
pose of contact, they are coated with fused ebonite mass or 
gutta-percha, only the loop in which the fork or spoon is hung 
and the upper end for suspending to the object-rod being left 
free. Silver wires are also better for this purpose. 

In order to secure an extra heavy coating of silver on the 
convex surfaces of spoons and forks which, being subject to 




384 ELECTRO-DEPOSITION OF METALS. 

greater wear than the other parts, require extra protection, 
some plating establishments use a frame in which the articles 
supported therein by their tips are placed horizontally in a 
shallow silver bath and immersed just deep enough to allow 
the projecting convexities to dip into the bath. By this arti- 
fice these portions are given a second coating of silver of any 
desired thickness. This mode of procedure, which is termed 
•' sectional " plating, accomplishes the intended purpose nicely 
and satisfactorily. In some establishments the silvered forks 
and spoons are placed between plates of gutta-percha of corre- 
sponding shape, and held together by rubber bands. In these 
plates the portions to be provided with an extra coating of 
silver are cut out. By suspending the forks and spoons thus 
protected in the bath, the unprotected places receive a further 
layer of silver, the outlines of which are later on smoothed 
down with burnishers. The second object may also be at- 
tained by coating the places which are to receive no further 
deposit with " stopping-off" varnish (see later on). 

According to German patent No. 76975, sheets of celluloid 
or similar substances are suspended as shields between the 
inside portions of spoons and the anodes. By this means the 
deposit of silver on these portions, which are subject to less 
wear, is only slightly augmented, while the outside portions 
acquire a heavier deposit. 

To attain the same object, J. Buck * suspends a frame in 
such a manner that every two spoons are turned with their 
inside portions towards each other, and anodes are arranged 
only on the outside portions. 

When commencing the operation of silver-plating, intro- 
duce into the bath at first a somewhat more powerful current, 
so that the first deposition of silver takes place quite rapidly 
and after 3 minutes regulate the current so that in 10 to 15 
minutes the objects are coated with a thin, dull film of silver. 
At this stage take them from the bath, and after seeing that 

* German patent 126053 (expired). 



DEPOSITION OF SILVER. 385 

•all portions are uniformly coated, scratch-brush them with a 
brass brush, which should, however, not be too fine. In 
doing this the deposit must not raise up. If at this stage the 
objects stand thorough scratch-brushing, raising of the deposit 
in burnishing later on need not be feared. 

Any places which show no deposit are vigorously scratch- 
brushed with the use of pulverized tartar, then again carefully 
-cleansed by brushing with lime-paste to remove any impuri- 
ties due to touching with the hands, pickled by dipping in 
potassium cyanide solution, again rinsed, quicked, and after 
-careful rinsing returned to the bath. Special care must be 
taken not to contaminate the bath with quick ing solution as 
this would soon spoil it. 

The objects now remain in the bath at a normal current- 
density until the deposit has acquired a weight corresponding 
to the desired thickness. Knives, forks and spoons receive a 
•deposit of 2.11 to 3.52 ozs. of silver per dozen. 

Considerable difficulty is sometimes experienced in silver 
plating the steel blades of table knives as the silver will strip 
•or pull off of the blade after it has been in use a short time. 
According to Mr. Charles H. Proctor* this difficulty is due to 
unsatisfactory conditions at the time of deposition. The coat- 
ing of the knives with copper previous to silver plating will 
not improve matters ; in fact this method has been discarded 
as a failure by all the manufacturers of silver-plated steel- 
knives and forks years ago. The most satisfactory method to 
pursue is to reduce all the silver from the surface of the knives 
by the aid of a strong cyanide solution and a strong reversed 
current of five to six volts or more. For cathodes use carbon 
and arrange the positive pole, upon which the knives are 
placed, so that the carbon cathodes will be placed on either 
side of the knives, as in a regular bath, so that the metal is 
reduced uniformly. After the silver is removed the surface is 
washed, dried and polished and then the knives should be 

-The Metal Industry, December, 1912. 
25 



386 ELECTRO-DEPOSITION OF METALS. 

boiled out in any of the usual alkaline solutions of potash or 
soda. Then immerse them in undiluted hydrochloric acid 
and wash and scour on a tampico wheel, using sodium carbon- 
ate in the water to prevent rusting after scouring. 

The articles are now ready for the bath. Frame up, wash 
in clean water, immerse in a 50 per cent, solution of hydro- 
chloric acid and water, rewash and immerse directly in the 
strike solution. This strike should consist of: Potassium 
cyanide 8 ozs., silver chloride J oz., water 1 gallon. 

The voltage should be from one to one and one-half volts 
with the full amperage of the dynamo, and the immersion 
from fifteen to thirty seconds. The knives should then be 
placed in the regular silver bath. This bath should have 
very little free cyanide and should be run at a voltage not 
exceeding one and one-half. The amperage should be about 
three per dozen of knives, or four amperes per square foot of 
exposed surface. This is the method used by the majority of 
the large concerns. 

Some platers use a first and second strike. In this case the 
first solution consists of a solution of cyanide in the propor- 
tion of six to eight ounces per gallon and one-eighth to one- 
quarter ounce of silver in the form of chloride. Two copper 
anodes are used, about three by eight inches, and two small 
silver anodes, about one-fourth the dimensions of the copper 
anodes. No deposit shows on the steel after the immersion in 
this strike. The knives are then immersed directly in the 
second strike, as before mentioned, and then into the bath. 
No copper should show from the copper and silver strike, and 
as soon as any becomes observable on the knives, more cya- 
nide should be added to the bath. This is practically only 
an electric cleaner. For the deposit of silver, by following 
the above instructions carefully, no trouble with peeling of 
the deposit will be experienced. 

Determination of weight. In order to control the weight of 
the deposit, proceed as follows : Remove one of the pans of a 
sensitive beam balance and substitute for it a brass rod which 



DEPOSITION OP SILVER. 



387 



keeps the other pan in equilibrium. Under this rod place a 
vessel filled with pure water, and of sufficient diameter and 
depth to allow of the article suspended to the rod dipping 
entirely into the water without touching the sides of the vessel. 
Suppose now that several dozen spoons of the same size and 
shape are at the same time to be provided with a deposit of 

Fig. 125. 




a determined weight, it suffices to control the weight of the 
deposit of a single spoon, and when this has acquired the 
necessary deposit all the other spoons will also be coated with 
a deposit of silver of the same thickness as the test spoon. The 
spoons having been quicked and carefully rinsed, one of them 
is suspended to the brass rod of the balance so that it dips en- 



388 



ELECTRO-DEPOSITION OF METALS. 



Fjg. 126. 



tirely under water. The equilibrium is then re-established by 
placing lead shot upon the pan of the scale, and adding the 
weight corresponding to the deposit the spoon is to receive. 
Now bring the weighed spoon together with the rest into the 
bath, and proceed with the silvering process in the ordinary 
manner. After some time the weighed spoon is taken from 
the bath, rinsed in water, and hung to the brass rod of the 
scale. If it does not restore the equilibrium of the latter, it is 
returned to the bath, and after some time again weighed, and 
so on until its weight corresponds to that of the lead shot and 
weight placed in the pan of the scale, when it is assumed that 
the other objects have also received their proper quantity and 
that the operation is complete. 

A more complete weighing apparatus is the metal! ometric 
balance first used by Brandely, and later on improved by 
Roseleur. The apparatus, which is shown in Fig. 125, is 
designed for obtaining deposits of silver " with- 
out supervision and with constant accuracy, 
and which spontaneously breaks the current 
when the operation is terminated." It is 
manufactured in various sizes, suitable for 
small or large operations. 

It consists of: 1. A w T ooden vat, the upper 
edge of which carries a brass winding-rod hav- 
ing a binding screw at one end to receive the 
positive conducting wire of the battery. From 
this rod the anodes are suspended, which are 
entirely immersed in the solution, and com- 
municate with brass cross-rods by means of 
platinum wire hooks. These cross-rods are 
flattened at their ends so that they may not 
roll, and at the same time have a better contact with the 
"winding-rod." 2. A cast-iron column screwed at its base 
to the side of the vat, and which carries near the top two pro- 
jecting arms of cast-iron, the extremities of which are vertical 
and forked, and may be opened or closed by iron clamps. 




DEPOSITION OF SILVER. 389 

These forks are intended for sustaining the beam and prevent- 
ing the knives from leaving their bearings under the influ- 
ence of too violent oscillations. In the middle of the two 
arms are two wedge-shaped recesses of polished steel to receive 
the knife edges of the beam. One of the arms of the column 
carries at its end a horizontal ring of iron in which is fixed 
a heavy glass tube supporting a cup of polished iron which is 
insulated from the column (Fig. 126). 

This cup has at its lower part a small pocket of lamb-skin 
or of India rubber, which by means of a screw beneath may 
be raised or lowered. This flexible bottom allows the opera- 
tor to lower or raise at will the level of the mercury intro- 
duced afterwards into t.he iron cup. Another lateral screw 
permits connection to be made with the negative electrode. 
3. A cast-iron beam carrying in the middle two sharp knife 
edges of the best steel hardened and polished. At each ex- 
tremity there are two parallel bearings of steel separated by a 
notch, and intended for the knife-edges of the scale-pan that 
receives the weights, and those of the frame supporting the 
articles to be plated. One of the arms of the beam is pro- 
vided with a stout platinum wire, placed immediately above 
and in the center of the cup of mercury. According as the 
beam inclines one way or the other, this wire plays in or out 
of the cup. 4. A scale-pan for weights, with two knife-edges 
of cast steel, which is attached to four chains supporting a 
wooden pan for the reception of weights. A smaller pan 
above is intended for the weights corresponding to that of the 
silver to be deposited. 5. The frame for supporting the 
articles to be plated, which is also suspended from two steel 
knife-edges, and the rod of which is formed of a stout brass 
tube attached below*to the brass frame proper, which last is 
equal in dimensions to the opening of the vat, and supports 
the rods to which the articles are suspended. 

It must, however, be borne in mind that the weight of a 
body immersed in water is less than when weighed in the air, 
it being as much less as the weight of the volume of fluid dis- 



390 ELECTRO-DEPOSITION OF METALS. 

placed by it. The specific gravity of silver is 10.5, hence 1 
cubic centimeter of silver weighs 10.5 more than 1 cubic 
centimeter of water, so that 10.5 grammes of silver weighed 
in the air weigh only 10.5 — 1=9.5 grammes when im- 
mersed in water. Since the specific gravity of the silver bath 
is greater than that of water — of fresh baths about 5° Be = 
1.035 — 10.5 grammes of silver, while immersed in the silver 
bath, weigh only 10.5 — 1.035 = 9.465 grammes. Hence for 
the determination of the weight to be placed in the scale-pan, 
which corresponds to the actual weight of the silver deposit, 
the desired weight of the deposit has to be multiplied by 9.465 
and divided by 10.5, or what amounts to the same thing, 
multiplied by 0.901. Suppose 300 grammes of silver are to 
be deposited upon forks, knives and spoons, not 300 grammes, 
but only 300 X 0.901 = 270.3 grammes have to be placed in 
the scale-pan. The weight of the articles themselves is not 
taken into account as the objects are tared under the solution 
and remain in the same bath-fluid to the end of the process. 
Hence, according to the above calculation, the weight, to be 
placed in the scale-pan should, in round figures, be 10 per 
cent, less than the desired weight of silver. However, as 
silver also deposits on the slinging wires, it has been shown 
that a reduction of 4 to 5 per cent, of the weight is about the 
right thing. 

• Fig. 127 shows a metallometric balance in operation, as 
coupled with the rheostat, voltmeter, and the silver bath, and 
will be understood without further explanation. These metal- 
lometric balances must of course be very carefully constructed 
so as to render possible accurate weighings with a load of 
about 11 lbs. They are used by most large silver-plating 
establishments for forks, knives and spoons. They may also 
be employed to advantage in plating coffee-pots, tea-pots, 
sugar bowls, etc., but with such articles special attention has 
to be paid to the anode arrangement in order to obtain a 
deposit of uniform thickness upon all portions. It is evident 
that with the use of straight silver anodes the portions of 



DEPOSITION OF SILVER. 



391 



round vessels nearest to the anodes will receive a thicker de- 
posit of silver than the portions at a greater distance from 
them. However, this also happens in every silver bath in 
operation not connected with a metallometric balance, the 
latter indicating of course only the total weight of deposit 
upon all the articles in the bath, and means for the formation 

Fig. 127. 




of a [uniform deposit on all portions must therefore be pro- 
vided. This is effected by the use of curved anodes suspended 
around the objects at equal distances; further by frequently 
changing the position of the objects so as to bring the more 
remote portions nearer to the anodes. 

For the determination of the weight of the deposit, Pfan- 



392 ELECTRO-DEPOSITION OP METALS. 

hauser Jr. uses a voltametric balance,* a combination of a 
voltameter with a balance, the principle of which, according 
to Ferchland,f is similar to Edison's registering voltameter,, 
and has for some time been practically utilized by Prof. 
Domalip J in Prague. 

A copper voltameter is an apparatus which allows of the 
determination of the quantity of current conducted in a cer- 
tain time through an acid copper sulphate solution (water 35 
ozs., copper sulphate 7 ozs., concentrated sulphuric acid If 
ozs., alcohol \ oz.) by the quantity of copper electrolytically 
separated on the cathode. Two copper anodes dip into the 
solution and between them is a copper cathode. The weight 
of the latter is exactly determined, and after the current has 
for an accurately measured time passed through the volta- 
meter, is washed with water, rinsed with alcohol, dried and 
again weighed. From the increase in weight the quantity of 
current which has passed through the voltameter can be 
readily calculated, since one ampere deposits in one hour 
1.1858 grammes of copper. 

Now by placing such a copper voltameter in the current- 
conductor of a silver bath so that the current passes through 
the bath and the voltameter one after the other, the same 
quantity of current must pass through the bath as well as the 
voltameter since, according to Kirchhoff's law, the current- 
strength is equally great in all points of a current-circuit. 
According to Faraday's law, the quantities of metals de- 
posited are proportional to their electro-chemical equivalents 
and hence the quantity of copper separated will be to the 
quantity of silver deposited as 1.858 : 4.0248 ; thus when the 
quantity of copper separated is known, the weight of the silver 
deposit can be readily calculated. 

In Pfanhauser's voltameter balance the copper cathode is- 

* German patent 120843. 

f Zeitschrift fur Elektrochemie, 1891, No. 71. 

X Ahrens, Handbuch der Elektrochemie, ii, Aufl. S. 151. 



DEPOSITION OF SILVER. 393 

by means of a conductor suspended to the metal-beam of a 
smaller balance, the equilibrium being restored by placing 
weights or shot in the scale-pan on the other end of the beam. 
Now in order to determine the weight adequate to the desired 
deposit in the silver bath, the weight has to be multiplied by 
1.1858 and divided by 4.0248. The number of grammes 
found is the weight the copper-deposit in the copper volta- 
meter must attain to correspond to the desired weight of the 
deposit in the silver bath. The weight thus determined has 
to be placed in the pan of the scale. When the deposit has 
acquired the desired weight the current is automatically in- 
terrupted by a contrivance similar to that described when 
speaking of the metallometric balance. 

As compared with the metallometric balance, the voltametric 
balance possesses advantages and disadvantages, the latter 
being chiefly that besides the swelling-up of the deposit in the 
voltameter, which has to be taken into consideration, the re- 
duction of the weight of silver to be deposited to the weight of 
the copper deposit to be placed in the scale-pan may readily 
lead to errors if left to the ordinary workman. To be sure,. 
this can be avoided by consulting tables which are furnished 
with the balance. 

It must furthermore be borne in mind that the voltametric 
balance gives reliable results only when the current-output of 
the silver bath remains constant and is exactly equal to that of 
the copper solution in the voltameter, a third correction of the 
weight being otherwise required. The current-output in the 
voltameter is 100, but that of fresh silver baths does not reach 
this height. According to numerous'determinations by Friess- 
ner, executed in Dr. G. Langbein & Co.'s electro-chemical 
laboratory, the current-output in cyanide silver baths varies 
according to whether the bath is at rest or in motion, the cur- 
rent-output with 0.3 ampere current-density being in a bath 
which contains per liter 25 grammes of silver as silver cya- 
nide and 27 grammes 99-percent potassium cyanide, 99.63 per 
cent, without agitation of the bath, and 99.18 per cent, with 
agitation, hence 0.45 per cent, less in the latter case. 



394 ELECTRO-DEPOSITION OP METALS. 

The increased electro-motive force when a voltametric bal- 
ance is placed in the current-circuit must also not be lost 
sight of. Since the voltameter solution and the silver bath 
are coupled one after the other, about double the electro- 
motive force is required, and this greater performance of work 
increases the cost of current. However, this is not of sufficient 
importance to prevent the use of voltametric balances. 

The advantages of a voltametric balance consist in that it 
is not necessar} 7 to place it in the vicinit} 7 of the bath. It may 
be located in a special dry room where it is not exposed to the 
effects of the damp atmosphere of the work-room. However, 
these effects are as a rule over-estimated, since metallometric 
balances with knife-edges of specially prepared steel, which 
quite well resists the action of rust, working in agate bearings, 
have been known to work with great accuracy after having 
been in use for fifteen years. The slighter load of the beams 
is also in favor of metallometric balances, so that the}' can be 
■of lighter construction. 

Metallometric as well as voltametric balances have the 
drawback that the current must pass through the beam and 
other sensitive parts to reach the bath. To prevent corrosion 
on the contacts and avoid large sparks on the sensitive por- 
tions, special protective measures are required which render 
the construction both more complicated and more expensive. 

The advantage of metallometric balances, namely, simple 
attendance and, when due care is observed, absolute certainty 
of results, may be advantageously utilized, together with the 
advantages of voltametric balances, i. e., slighter load and 
location at any desired distance from the bath, by the follow- 
ing combination devised b} 7 Neubeck. 

If in front of the silver bath be placed a smaller controlling 
bath of exactly the same composition as the silver bath in 
operation, or in other words, is taken from the latter, the cur- 
rent-output of both these baths must be the same, provided 
the current-density is the same. Now by using as cathodes 
for this controlling bath very thin silver sheets — 0.05 to 0.1 



DEPOSITION OF SILVER. 



395 



millimeter thick — with a total surface approximately equal to 
that of the objects in the bath, the weight of the cathodes will, 
on the other hand, be materially less than that of the articles 
in the bath, for instance, of an equally large surface repre- 
sented by spoons, and consequently the balance can be of 
lighter construction, while, on the other hand, the current- 
density in the controlling bath will be approximately equal 
to that in the silver bath. 

One dozen spoons w r eigh on an average 540 to 550 grammes 
and have a surface of about 13.2 square decimeters. The same 

Fig. 128. 




surface in silver sheet, 0.1 millimeter thick, weighs about 70 
grammes, and in silver sheet, 0.05 millimeter thick, about 35 
grammes. Hence the load of the ware is, in the commence- 
ment, 7J to 15 times less than with the metallometric balance 
and when, on attaining a thickness of about J millimeter, the 
cathodes are reversed, always only half as great. 

Now by allowing the current to pass through the control- 
ling bath and then through the silver bath, exactly the same 
quantity of silver is deposited in the former as in the latter; 



396 ELECTRO-DEPOSITION OF METALS. 

thus by connecting the cathodes of the controlling bath with 
a balance, the quantity of metal deposited in the silver bath 
upon the objects can be accurately determined. 

These considerations led to the construction of the volta- 
metric controlling apparatus, Fig. 128, which can be connected 
with any kind of cheap beam-balance. The apparatus * con- 
structed by Dr. G. Langbein & Co. is arranged as follows : 

The screw 1 secured to the anode-frame (Fig. 128) is directly 
connected with the anode wire. Upon the anode-frame of 
copper sit the conducting rods 9, 9, 9, etc., for the anodes, the 
latter being secured to them by means of platinum wire. To 
the rod 16 is secured the movable cathode from 7, to which 
the thin cathode sheets are suspended by means of platinum 
wire. The current enters the bath through the binding-post 
1, the anode-rods 9, and the anodes, passes to the cathodes, 
and returns through the cathode-frame 7 to the source of cur- 
rent so long as the screw 2 fixed to the support 17 dips, by 
reason of the load of the balance, into the mercury vessel 3.. 
The latter is secured to the anode-frame 7 and conductively 
connected with it. The celluloid disk 10 serves the purpose 
of protecting the bath from mercury, which may be spilled by 
careless handling, passing into it. 

When the cathodes have attained the required weight the 
flow of current to the bath is interrupted by the beam of the 
balance tilting over. The two steel pins 4 and 5, which are 
insulated from the mercury vessel 3, dip thereby into the mer- 
cury cups 6 fixed below them on the movable arm of the 
support 17 and insulated one from the other, the short-circuit 
of the bell wire being thus effected. The wire 11 leads direct 
to the bell 13, while a second wire 12 leads through the spirals 
14 to the support 17 and from there through spiral 15 to the 
bell. When the pins 4 and 5 dip into the mercury cups, 6, a 
second connection with the bell is made and the latter rings 
so long as the pins 4 and 5 dip into the mercury. 

* German patent. 



DEPOSITION OF SILVER. 397 

Contrary to the principle of the metallometric and the volta- 
metric balances, the beam and other portions of the balance 
are here entirely excluded from the current-circuit. Hence, 
any ordinary beam-balance can be used and no corrosion of 
sensitive portions of the balance by sparks takes place. 

When the cathodes of the controlling bath have attained a 
thickness approximately the same as that possessed by the 
silver anodes of the bath in the commencement of the opera- 
tion, they are used as anodes by suspending them to the 
anode-rods, while the anodes"* which have become thinner are 
suspended as cathodes. 

With this arrangement there is to be sure, the same draw- 
back as with the voltametric balance, namely, that by reason 
of the baths being coupled one after the other, double the 
electro-motive force than that used for a silver bath connected 
with a metallometric balance is required. The interest, which, 
however, amounts to very little, on the dead metallic silver in 
the controlling bath may also be called a disadvantage. On 
the other hand, the controlling apparatus has the advantage 
that two or more silver baths of the same composition can be 
connected with it when the same quantity of silver is to be 
deposited upon approximately the same object-surface in each 
bath. 

The case is somewhat different when the baths in operation 
are of considerable size and furnished with many object-rods. 
In order to obtain the same current-density in the actual silver 
bath as in the controlling bath, the latter would have to be of 
quite large dimensions and require so much electrode-material 
as to cause considerable expense for providing it. In such a 
case the advantages presented by the same composition of the 
operating bath and the controlling bath have to be abandoned 
and the controlling bath has to be used as a copper voltameter. 
Since in the copper solution depositions can be made with cur- 
rent-densities up to 1.5 amperes per square decimeter only one- 
fifth part of the object-surface in the operating bath is required 
as cathode surface in the controlling copper bath. Of course 



398 ELECTRO-DEPOSITION OF METALS. 

the weight of the desired silver deposit, reduced to copper, 
which is found from tables furnished with the apparatus, has 
to be placed in the scale-pan. The tables are calculated for 
current-outputs of from 98 to 99.6 per cent, in T \ per cent, for 
baths for silvering by weight with 25 grammes of fine silver 
as silver cyanide and 25 grammes of 99-percent potassium 
cyanide, and a current-density of 0.3 ampere per square deci- 
meter. Hence the current-output of the bath to be used has 
to be determined, and the weights of copper corresponding to 
the silver deposit are then found in the table for the deter- 
mined current-output. As the current-output is subject to 
change by the bath becoming gradually contaminated by for- 
eign metals, which cannot be avoided in silvering metals 
soluble in potassium cyanide, for instance, zinc and copper, 
it will be necessary to determine the current-output at least 
twice a year. 

As previously mentioned, the current-output is materially 
smaller when the bath is agitated than when it is at rest, and 
hence the controlling silver bath cannot be used for agitated 
baths because, in order to obtain accurate weighing results, 
agitation of the controlling bath has to be avoided. In this 
case the copper solution (see p. 392) has also to be used 
with reference to the tables for the respective current-output. 
However, when the controlling apparatus works with the cop- 
per solution, it still has the advantage of no current passing 
through sensitive portions of the balance, and thus they are 
not subject to wear. 

Calculation of the weight of the silver deposit from the current- 
strength used. This can be done if the current conducted into 
the bath during silvering be constantly kept at the same 
strength, and the current-output of the bath be taken into 
consideration. According to the table on p. 61, one ampere 
deposits in 1 hour 4.0248 grammes of silver, hence after t 
hours with a current-strength i : 4.0248 X i X t grammes of 
silver will be deposited, if the current-output amounts to 100. 
However, the latter is, as a rule, only 98 to 99 per cent., and 



DEPOSITION OF SILVER. 399' 

the value obtained is therefore to be multiplied by the frac- 
tion -n^ - or -j^o, in order to determine the actual weight of the 
deposit. 

Attention must, however, be drawn to the fact that it is 
very difficult to keep the current-strength quite constant for a 
longer time, especially where numerous baths are connected 
to a common circuit, and for this reason a calculation, based 
upon the measurement of the current-strength, will very likely 
be in most cases impracticable. 

For the calculation of the time which has been consumed 
for depositing a certain weight of silver when the current- 
strength is known, the desired weight of the deposit has to be 
divided by the product from current-strength times chemical 
equivalent of the silver, and the value found multiplied by 

100 p-v. 100 

9 8 Ui 99 • 

If, for instance, 50 grammes of silver are to be deposited 
upon one dozen spoons, and the current-strength be 3.2: 
amperes and the current-output 99 per cent., the time is found 
from the following calculation : 

QO 50 A X J A ° Q - = ^ = 3.92 hours = 3 hours 55 
3.2 X 4.0248 X 99 1275.05 

minutes. 

If the current-strength is to be calculated, which is required 

to produce in a given time a determined thickness of deposit, 

the product from the desired thickness in millimeters, times 

the object-surface in square decimeters, times the specific 

gravity of the metal to be deposited, times 1000, has to be 

divided by the product from time, times electro-chemical 

equivalent, times current-output. Suppose, for instance, the 

desired thickness of the deposit is to be 0.1 millimeter, the 

object-surface 1.5 square decimeter, the specific gravity 10.5, 

the time 4 hours, the electro-chemical equivalent 4.025, and 

the current-output 98 per cent., then the current-strength 

required is: 

0.1 X 1.5 X 10.0 X 100 1575 



4 x 4.0248 X 98 ' 1577.72 



= 0.99 ampere. 



400 ELECTRO-DEPOSITION OF METALS. 

When the articles have received a deposit of the required 
weight, they are treated for the prevention of subsequent yel- 
lowing according to one of the methods given on p. 379, then 
scratch-brushed bright with the use of decoction of soap-root, 
plunged in hot water and dried in sawdust. 

Mat silver. — Articles which are to retain the beautiful crys- 
talline dead white with which they come from the bath are, 
without touching them with the fingers or knocking them 
against the sides of the vessel, rinsed thoroughly in clean 
water, plunged into very hot, distilled water, and then sus- 
pended free to dry. Immediately after drying they are to be 
provided with a thin coat of transparent lacquer to protect the 
dead-white coating, which readily turns yellow, and, more- 
over, is very sensitive. 

Frosting silver is affected by means of scratch-brushes. They 
take different forms, according to the kind of work to be 
frosted. They are made of several strengths, that is, the 
wires of them are especially prepared of several thicknesses, 
and when a very fine satin finish is required, a brush of very 
fine wire is taken, and so on. A brush with wires thicker 
and thicker in proportion is taken as a more extended rough- 
ness is desired. These wire brushes are fixed upon a hori- 
zontal spindle in the lathe. Frosting requires great speed to 
do the work nicely. The wires of the scratch-brush must be 
even on the surface, all of the same length, and always kept 
straight at the points, otherwise the frosting will not be 
regular. Sometimes the little hand scratch-brushes are 
employed for coarser work; four of them are taken, and firmly 
secured in four corresponding grooves in a circular chuck, 
which screws into the lathe. The ends of the four little 
brushes are repeatedly cut off as occasion requires in order to 
present a straight surface for continual contact with the work, 
without which it w T ould not present a uniform appearance. 

According to Gee, the following mixture may also be used 
for frosting silver: Sulphuric acid 1 oz., water 1 oz., saltpetre 
2 dwts. Add the sulphuric acid to the water and afterwards 



DEPOSITION OF SILVER. 401 

put in the saltpetre in a state of fine powder. The mixture is 
used in the boiling state and takes a few minutes to accom- 
plish the desired object. 

Polishing the deposits. — The silvered articles having been 
scratch-brushed, must finally be polished, which may be 
effected upon a fine felt wheel with the use of rouge, but im- 
parting high luster by burnishing is to be preferred, the de- 
posit being first treated with the steel burnisher, and then 
with the stone burnisher, as explained on p. 216. 

In some establishments in which plated table-ware in large 
•quantity is turned out, ingeniously-devised burnishing ma- 
chines driven by power are in use, by which much of the 
manual labor is saved. The knife, spoon, etc., each supported 
by its tips in a suitable holder, are very slowly rotated, while 
the burnishing-tool moves quickly over the surface, perform- 
ing the work rapidly and satisfactorily. 

When burnishing is completed, the surface is wiped off lon- 
gitudinally with an old, soft calico rag. Sawdust, hard cloth, 
and tissue paper produce streaks. 

B. Ordinary silver-plating. — Objects which are to receive a 
deposit of less thickness have to undergo exactly the same 
operations described under plating by weight, the only differ- 
ence being that for quicking a weaker solution (15 to 31 
grains of nitrate of mercur}^ to 1 quart of water), or very 
dilute solution of potassium-mercury cyanide (77 grains of 
potassium-mercury cyanide and 77 grains of potassium cya- 
nide to 1 quart of water) is used, and that the objects remain 
a shorter time in the bath. 

Direct silvering of Britannia, tin, German silver. As pre- 
viously mentioned, iron, steel, zinc and tin should first be 
coppered or brassed. However, tin and Britannia may also 
be directly plated, but the bath must be rich in silver and 
contain a large excess of potassium cyanide. Further, the 
current should be so strong that the articles acquire a blue- 
gray color. They are then suspended in the silver bath of 
normal composition, and plating is finished with a normal 
current. 
26 



402 ELECTRO-DEPOSITION OF METALS. 

The same process is also suitable for plating articles of Ger- 
man silver rich in nickel. In polishing such articles it is fre- 
quently observed that the deposit rises, but by plating in the- 
above-mentioned preparatory bath, and finishing in the nor- 
mal bath, the deposit will very well bear polishing with the- 
steel. 

For silver-plating Britannia ware and articles of tin, Gore 
recommends the following process. Boil the articles in caustic 
potash solution, scratch-brush them, and plate them prepara- 
tively with a strong current and the use of large anode- 
surfaces in a hot silver bath (194° F.), and then finish depo- 
sition to the desired thickness in the ordinary cold silver bath. 

According to an Australian patent, the following process is 
claimed to yield good results in directly silver-plating won and 
steel: The article to be plated having first been dipped in hot 
dilute hydrochloric acid is brought into solution of mercury 
nitrate and then connected with the zinc pole of a Bunsen. 
element. It becomes quickly coated with a layer of mercury,. 
when it is taken out, washed and brought into an ordinary 
silver bath. When covered with a layer of silver of sufficient 
thickness, it is heated to 572° F., the mercury evaporating at 
this temperature. It is claimed that silver deposited in this 
manner adheres more firmty than by any other process, but 
it is doubtful whether for solid silver-plating this method can 
replace previous coppering. 

Stopping off. If certain parts of a metallic article are not to. 
receive a deposit, as for instance, when a contrast is to be 
effected by depositing different metals upon the same object, 
these parts are covered, or " stopped-off," with a varnish. 
Stopping-off varnish is prepared by dissolving asphalt or dam- 
mar with an addition of mastic in oil of turpentine. Apply 
with a brush, and after thoroughly drying the articles in the 
drying-chamber, place them for an hour in very cold water, 
whereby the varnish hardens completely. After plating, the 
varnish is removed, best with benzine, the articles plunged in 
hot water and dried in sawdust. 



DEPOSITION OF SILVER. 403 

For a varnish that will resist the solvent power of the hot 
alkaline gilding liquid, Gore recommends the following com- 
position : Translucent rosin 10 parts, yellow beeswax 6, extra- 
fine red sealing-wax 4, finest polishing rouge 3. 

Quick-drying, stopping-ofF varnishes, which harden imme- 
diately at the ordinary temperature and resist cyanide baths, 
are now found in commerce. 

Special applications of electro-silvering. — It remains to men- 
tion a few special applications of electro-silvering as well as 
processes of decorating with silver by electrical and chemical 
means. 

Silvering of fine copper wire is effected in an apparatus, which 
is described and illustrated in Chapter IX, " Deposition of 
Gold," where further details will be found. Luster is im- 
parted to the silvered wire by drawing through a draw-plate. 

Incrustations with silver (and gold, and other metals). — By in- 
crusting is understood the inlaying of depressions, produced by 
engraving or etching upon a metallic body, with silver, gold 
and other metals, such as Japanese incrustations, which are 
made by mechanically pressing the silver or gold into the de- 
pressions. Such incrustations, however, can also be produced 
by electro-deposition, the process being as follows: The design 
which is to be incrusted upon a metal is executed with a pig- 
ment of white-lead and glue-water or gum-water. The portion 
not covered by the design is then coated with stopping-off 
varnish. The article is next placed in dilute nitric acid, 
whereby the pigment is first dissolved, and next the surface 
etched, which is allowed to progress to a certain depth. 
Etching being finished, the article is washed in an abundance 
of water and immediately brought into a silver or gold bath, 
in which, by the action of the current, the exposed places 
are filled up with metal. This being done, the stopping-off 
varnish is removed with benzine, the surface ground smooth, 
and polished. In this manner one article may be incrusted 
w T ith several metals; for instance, brass may be incrusted with 
copper, silver and gold, and by oxidizing or coloring portions 



404 ELECTRO-DEPOSITION OF METALS. 

of the copper beautiful effects can be produced. The prin- 
cipal requisites for these incrustations are manual skill and 
much patience. Expensive apparatus is not required, every 
skilled electro-plater being able to execute the work. 

Imitation of niel or nielled silvering. By nielling is under- 
stood the inlaying of designs produced either by engraving or 
stamping, with a black mixture of metallic sulphides. The 
nielling powder is prepared by melting silver 20 parts by 
weight, copper 90 parts and lead 150 parts. To the liquid 
metallic mass add 26 \ ozs. of sulphur and f oz. of ammonium 
chloride, quickly cover the crucible and continue heating until 
the excess of sulphur is volatilized. Then pour the contents 
of the crucible into another crucible, the bottom of which is 
-covered about \ inch deep with flowers of sulphur, cover the 
<crucible and allow the mixture to cool. When cold bring the 
'Contents once more to the fusing point, and pour the fused 
mass in a thin stream into a bucket filled with water, whereby 
granulated metal is formed, which can be readily reduced in 
:a mortar to a fine powder. This powder is mixed with am- 
monium chloride and gum-water to a thin paste. This paste 
is brought into the designs produced by engraving or stamp- 
ing, and after drying burnt-in in a muffle. When cold, any 
roughness is removed by grinding, and after polishing a 
sharp, black design in white silver is obtained. 

To imitate niel by electro-deposition, the design is executed 
■upon the surface with a pigment consisting of white lead and 
glue- or gum-water. The portions which are to remain free 
are coated with stopping-off varnish, and the design is un- 
covered by etching with very dilute nitric acid. The article 
is then brought as the anode into dilute solution of ammonium 
sulphide, while a small sheet of platinum connected to the 
negative pole is dipped into the solution. Sulphide of silver 
being formed, the design becomes rapidly black-gray, and 
after removing the stopping-off varnish with benzine, stands 
■out in sharp contrast from the white silver. 

Upon brass, nielling may be imitated by silvering the 



DEPOSITION OP SILVER. 405 

article and then engraving the design, by which the silver 
is removed and the brass uncovered. The article is then 
brought into the black bright-dip, by which the uncovered 
brass is colored black while the silvered portions remain un- 
changed. If portions in relief are to be made black, the sil- 
vering is removed by grinding, the article dipped into cream 
of tartar solution, and then brought into the black bright-dip. 
This process is largely employed by manufacturers of buttons 
when silvered buttons are to be supplied with the name of the 
firm and the quality number in black. 

Old {antique) silvering. — To give silvered articles an antique 
appearance coat them with a thin paste of 6 parts graphite, 1 
red ochre and sufficient spirits of turpentine. After drying, 
gentle rubbing with a soft brush removes the excess of powder, 
and the reliefs are set off (discharged) by means of a rag 
dipped into alcohol. 

A tone resembling antique silvering is also obtained by 
brushing the silvered articles with a soft brush moistened with 
very dilute alcoholic solution of chloride of platinum. 

In order to impart the old silver tinge to small articles, 
such as buttons, rings, etc., they are agitated in the above- 
mentioned paste, and then "tumbled" with a large quantity 
of dry sawdust until the desired shade is obtained. 

With the use of the electric current and carbon anodes, 
antique silver may be produced as follows : Bring the silvered 
articles, previously thoroughly freed from grease, into the 
silver bath at an electro-motive force of 4 to 5 volts, and allow 
them to remain for a few minutes until they become covered 
with a uniform blue-gray deposit. They are then thoroughly 
rinsed in water, and the raised portions rubbed with very fine- 
pumice, to lay bare the silver. If surfaces are to appear in 
antique silver, the deposit is only sufficiently removed with 
pumice for the silver to shine through, and the surface to 
show the proper antique-silver tone. 

Oxidized silvering. This term is incorrect, as silver oxide 
does not form the coloring film or at least only to a very 



406 ELECTRO-DEPOSITION OP METALS. 

slight extent, the coloration being due to the formation of 
silver sulphide or silver chloride upon the objects. This pro- 
cess of coloring silver is frequently employed to obtain dec- 
orative contrasts. Solution of pentasulphide of potassium 
(liver of sulphur of the shops) is generally used for the pur- 
pose. Dissolve liver of sulphur 1 oz., and ammonium car- 
bonate 2 ozs., in 1 gallon of water heated to 176° F. Immerse 
the objects in the solution and allow them to remain until they 
have acquired the desired dark tone. Immediately after im- 
mersion the articles become pale gray, then darker, and 
finally deep black blue. For coloring in this manner, the 
silvering should not be too thin. For objects with a very 
thick deposit of silver, solution of double the strength may be 
used. Very slightly silvered objects cannot be colored in this 
manner, as the bath would remove the silvering, or under the 
most favorable conditions produce only a gray color. If the 
operation is not successful, and the objects come from the 
bath stained or otherwise, dip them in warm potassium 
cyanide solution, which rapidly dissolves the silver sulphide 
formed. 

A bath which produces the same effect as potassium sul- 
phide solution may be cheaply prepared as follows : Pour 1 
quart of water over 13 ozs. of unslaked lime and 22J ozs. 
flowers of sulphur. The mixture becomes quickly heated 
and thick. Dilute it with 1 quart hot water and boil half an 
hour. The resulting liquor is now ready for use and is best 
employed very hot. If, whilst boiling the solution, If ozs. of 
antimonious sulphide or If ozs. of arsenious sulphide be added, 
an agreeable bluish-gray coloration is obtained which, with 
the use of antimonious sulphide passes later on into a beauti- 
ful graj'-brown. 

A beautiful brown tone is imparted to silver objects by im- 
mersion in the following solution : Copper sulphate 10 ozs., 
saltpetre 5 ozs., ammonium chloride 10 ozs. 

Another process is as follows : Place the objects in a porce- 
lain dish, cover them with ammonium sulphide, and heat 



DEPOSITION OF SILVER. 407 

gradually. When the objects have acquired a blue-black 
color, take them from the dish, place them in soap- water and, 
so long as they remain in the latter, rub them with a soft 
brush. 

A yellow color is imparted to silvered articles by immersion 
in a hot saturated solution of copper chloride, rinsing and 
drying. 

For silvering by contact, boiling and friction, see special chap- 
ter " Depositions by Contact." 

Stripping silvered articles. — AVhen a silvering operation has 
failed, or the silver is to be stripped from old silvered articles, 
different methods have to be used according to the nature of 
the basis-metal. Silvered iron articles are treated as the anode 
in potassium cyanide solution in water (1 : 20), the iron not 
being attacked by potassium cyanide. As cathode suspend 
in the solution a few silver anodes or a copper-sheet rubbed 
with an oily rag ; the silver precipitates upon the copper 
sheet but does not adhere to it. Articles, the basis of which 
is copper, are best stripped by immersion in a mixture of 
equal parts of anhydrous (fuming) sulphuric acid and nitric 
acid of 40° Be. This mixture makes the copper passive, it 
not being attacked while the silver is dissolved. Care must, 
■however, be had not to introduce any water into the acids, 
nor to let them stand without being hermetically closed, since 
by absorbing moisture from the air they become dilute, and 
may then exert a dissolving effect upon the copper. The 
fuming sulphuric acid may also be highly heated in a shallow 
pan of enameled cast iron. Then at the moment of using it 
pinches of dry and pulverized nitrate of potassium (saltpeter) 
are thrown into it, and the article, held with copper tongs, is 
plunged into the liquid. The silver is rapidly dissolved, 
while the copper or its alloys is but slightly corroded. Ac- 
cording to the rapidity of the progress of solution, fresh addi- 
tions of saltpeter are made. All the silver has been dissolved 
when, after rinsing in water and dipping the articles into the 
cleansing acids, they present no brown or black spots, that is 



408 ELECTRO-DEPOSITION OP 1 METALS. 

to say, when they behave like new. In this hot acid stripping: 
proceeds more quickly than in the cold acid mixture, but the 
latter acts more uniformly. 

Determination of silver-plating. — By applying to genuine- 
silver-plating a drop of nitric acid of 1.2 specific gravity, in. 
which red chromate of potash has been dissolved to satura- 
tion, a red stain of chromate of silver is formed. According to 
Grager, this method ma}' also be used, to a certain extent for 
the recognition of any other white metal which may be mis- 
taken for silver. A drop of the mixture applied to German 
silver becomes brown, no red stain appearing after rinsing 
with water; upon Britannia the drop produces a black stain; 
zinc is etched without a colored spot remaining behind ; upon 
amalgamated metals a brownish precipitate is formed, which 
does not adhere and is washed away by water; upon tin the 
drop also acquires a brownish color, and by diluting with 
water a yellow precipitate is formed ; upon lead a beautiful yel- 
low precipitate is formed. 

Custom-house officers in Germany are directed by law to 
use the following process for the determination of genuine sil- 
ver-plating : Wash a place on the article with ether or alco- 
hol, dry with blotting paper, and apply to the spot thus 
cleansed a drop of a 1 to 2 per cent, solution of crystallized bi- 
sulphite of soda prepared by boiling 1.05 ozs. of sodium sul- 
phite and 2.36 drachms of flowers of sulphur with 0.88 oz.. 
of water until the sulphur is dissolved, and diluting to 1 
quart of fluid. Allow the drop to remain upon the article 
about ten minutes and then rinse off with water. Upon sil- 
ver articles, a full, round, steel-gray spot is produced. Other 
white metals and alloys, with the exception of amalgamated 
copper, do not show this phenomenon, there appearing at the- 
utmost a dark ring at the edge of the drop. Amalgamated 
copper is more quickly colored, and acquires a more dead- 
black color than silver. 



DEPOSITION OP SILVER. 409 

Examination of silver baths. 

For the quantitative examination of silver baths, the deter- 
mination of the content of free potassium cyanide and of me- 
tallic silver as well as of the potassium carbonate which is 
formed by the action of air, etc., upon the potassium cyanide, 
has to be taken into consideration. 

Regarding the determination of the free potassium cyanide, 
the reader is referred to the method given under " Examina- 
tion of copper baths containing potassium cyanide," and what 
has been said there in reference to replacing the deficiency 
also applies here. 

The potassium carbonate which is formed in constantly in- 
creasing quantities in the bath, is best removed by the ad- 
dition of barium cyanide solution, whereby, in consequence of 
reciprocal decomposition, potassium cyanide is formed, while 
barium carbonate in an insoluble state is separated. 

The determination of the potassium carbonate present in the 
bath is desirable, so as to be able on the one hand, to calcu- 
late the quantity of barium cyanide required for its decompo- 
sition and, on the other, to become acquainted with the 
quantity of free potassium cyanide formed thereby. 

The determination of the potassium carbonate is effected as 
follows: Bring by means of the pipette, 20 cubic centimeters 
of silver bath into a beaker, dilute with 50 cubic centimeters 
of water, and compound with barium nitrate solution in ex- 
cess. Allow to settle for some time, then filter through not 
too large a paper filter, taking care that the entire precipitate 
reaches the filter, and wash the filter thoroughly with water 
until a few drops of the filtrate, when evaporated upon a 
platinum sheet, leave no residue. Now take the filter, to- 
gether with the residue, carefully from the funnel, bring it 
into a beaker, and add water, as well as a carefully measured 
quantity of standard nitric acid, which should, however, be 
somewhat larger than required for dissolving the barium car- 
bonate. While solution is being effected, keep the beaker 



410 ELECTRO-DEPOSTTION OF METALS. 

covered with a watch glass, and then rinse any drops appear- 
ing upon the latter into the beaker by means of distilled 
water. Add to the solution, as an indicator, a few drops of 
methyl-orange, whereby the solution is colored red, and add, 
while stirring constantly, from a burette, standard soda solu- 
tion until the red color of the solution passes into yellow. By 
now deducting the cubic centimeters of soda solution used 
from the cubic centimeters of standard nitric acid added to 
the solution of the barium carbonate, and multiplying the 
number of the remaining cubic centimeters of standard nitric 
-acid by 3.45, the quantity of potassium carbonate in grammes 
present in 1 liter of silver bath is obtained. 

Now the quantity of barium cyanide has to be calculated, 
which is required for the conversion of the quantity of potas- 
sium carbonate found, into potassium cyanide with the separa- 
tion of barium carbonate. It is best to use a 20J per cent, 
barium cyanide solution, and since 1 gramme of potassium 
carbonate requires for conversion 1.36 grammes of barium 
cyanide, 6.80 grammes of 20 per cent, barium cyanide solution 
are necessary for the purpose, and each gramme of potassium 
•carbonate yields 0.942 gramme of potassium cyanide. Hence 
for the determination of the potassium cyanide present after 
the destruction of the potassium carbonate, there has to be 
added to the potassium cyanide found by titration, the content 
of free potassium cyanide calculated from the conversion with 
barium cyanide. If this shows a deficit as compared with the 
original content, it is to be made up by adding only about 
one-half the quantity, for the same reason as given in speak- 
ing of the copper bath, namely, because the potassium for- 
mate, which is at the same time formed, performs the function 
of the potassium cyanide. 

To save calculation a table b}' Steinach and Buchner for 
the use of a 20^ per cent, barium cyanide solution is here 
.given : 



DEPOSITION OF SILVER. 



411 







For 1 liter of si 


lver bath have to be 


added 


Potassium 


carbonate in 












1 liter of silver bath. 


20£ per cent. 


barium 


cya- 


Potassium 


cyanide 






nide solution. 




formed thereby. 


1 


gramme 


6.7 grammes 




0.95 gramme 


2 


it 


13.4 


a 




1.90 


a 


3 


a 


20.1 


tt 




2.85 


a 


4 


tt 


26.8 


a 




3.80 


a 


5 


tt 


33.5 


a 




4,70 


a 


6 


; t 


40.2 


a 




5.70 


a 


7 


a 


46.9 


it 




6 65 


tt 


8 


a 


53.6 


a 




7.60 


" 


9 


ti 


60.3 


a 




8.55 


tt 


10 


a 


67.0 


tt 




9.50 


a 


11 


a 


73.7 


it 




10.40 


it 


12 


a 


80.4 


it 




11.40 


a 


13 


it 


87.1 


a 




12.35 


a 


14 


it 


93.9 


a 




13.30 


it 


15 


a 


100.5 


tt 




14.20 


it 



For the determination of the silver, the electrolytic method is 
the most simple and suitable in so far as the silver bath can 
be directty used for the purpose. 

Bring by means of the pipette into the platinum dish 10 
cubic centimeters of the silver bath, or 20 cubic centimeters 
if the bath is weak ; add, according to the greater or smaller 
excess of the potassium cyanide present, J to 1 gramme of 
potassium cyanide dissolved in water, and dilute up to 1 or If 
centimeters from the edge of the dish. Heat, by means of a 
small flame, the contents of the dish to from 140° to 149° F., 
•and maintain this temperature as nearly constant as possible. 
Electrolysis is effected with a current-density ND 100 = 0.08 
ampere. Complete precipitation, which requires 3 to 3J 
hours, is recognized by ammonium sulphide producing no 
•dark coloration of the fluid. The dish is then washed, with- 
-out interrupting the current, rinsed with alcohol and ether, 
dried for a short time at 212° F., and weighed. The weight 
of the precipitate multiplied by 100 gives the content of silver 
in grammes per liter of bath. If 20 cubic centimeters of silver 
bath have been electrolyzed, multiply only by 50. 



412 ELECTRO-DEPOSITION OF METALS. 

If the analysis has shown a deficit of silver in the bath, it 
can be readily replaced. For strengthening the bath it is best 
to use pure crystallized potassium-silver cyanide, which in 
round numbers contains 50 per cent, of silver. Suppose the 
bath contains per liter 2 grammes of silver less than it should, 
then for each liter of bath (52 : 100 = 2 : x ; x = 3.8 grammes),. 
3.8 grammes of pure crystallized potassium-silver cyanide have 
to be added. 

The more troublesome volumetric analysis may be omitted, 
it offering no advantage over the electrolytic method. 

Recovery of silver from old silver baths, etc. — Old solutions 
which contain silver in the form of a silver salt are easily 
treated. It is sufficient to add to them, in excess, a solution 
of common salt, or hydrochloric acid, when all the silver 
will be precipitated in the state of chloride of silver, which r 
after washing, may be employed for the preparation of new 
baths. 

For the recovery of silver from solutions which contain it as- 
cyanide. the solutions may be evaporated to dryness, the resi- 
due mixed with a small quantity of calcined soda and potas- 
sium cyanide, and fused in a crucible, whereby metallic silver 
is formed, which, when the heat is sufficiently increased, will 
be found as a button upon the bottom of the crucible ; or if it 
is not desirable to heat to the melting-point of silver, the 
fritted mass is dissolved in hot water, and the solution con- 
taining the soda and cyanide quickly filtered off from the 
metallic silver. The evaporation of large quantities of fluid, 
to be sure, is inconvenient, and requires considerable time. 
But the reducing process above described is without doubt the 
most simple and least injurious. 

According to the wet method, the bath is strongly acidulated 
with hydrochloric acid, provision being made for the effectual 
carrying-off of the hydrochloric acid liberated. Remove the- 
precipitated chloride of silver and cyanide of copper by filtra- 
tion, and, after thorough washing, transfer it to a porcelain 
dish and treat it, with the aid of heat, with hot hydrochloric 



DEPOSITION OF SILVER. 413 

acid, which will dissolve the cyanide of copper. The result- 
ing chloride of silver is then reduced to the metallic state by 
mixing it with four times its weight of crystallized carbonate 
of soda, and half its weight of pulverized charcoal. The whole 
is made into a homogeneous paste, which is thoroughly dried, 
and then introduced into a strongly-heated crucible. When 
-all the material has been introduced, the heat is raised to pro- 
mote complete fusion and to facilitate the collection of the 
separate globules of silver into a single button at the bottom 
of the crucible, where it will be found after cooling. If gran- 
ulated silver is wanted, pour the metal in a thin stream and 
from a certain height, into a large volume of water. 

A ver}' simple method is as follows : Bring the silver bath 
into flasks, mix the contents of the flask with zinc dust (zinc 
in a finely-divided state) in the proportion of about ^ oz. per 
quart of bath, and shake thorough^ 5 or 6 times every day. 
In five days all the silver is precipitated. Decant the clear 
liquid from the precipitate, wash the latter several times with 
water, and dissolve the zinc contained in the precipitate in 
pure hydrochloric acid. The silver remains behind in a pul- 
verulent form, and may be dissolved in nitric acid, and worked 
up into silver chloride or silver cyanide. In place of zinc, 
aluminium powder may be used for precipitation, the excess 
of aluminium being then dissolved by caustic potash, or 
caustic soda solution. 

From acid .mixtures used for stripping, the silver may be 
obtained as follows: Dilute the acid mixture with 10 to 20 
times the quantity of water, and precipitate the silver as 
chloride of silver by means of hydrochloric acid. Interrupt 
the addition of hydrochloric acid, when a drop of it produces 
no more precipitate of chloride of silver in the clear fluid. 
The precipitated chloride of silver is filtered off, washed, and 
either directly dissolved in potassium cyanide, or the silver is 
regained as metal by fusing the chloride of silver with cal- 
cined soda and wood charcoal powder, previously thoroughly 
mixed. 



414 ELECTRO-DEPOSITION OF METALS. 

Still more simple is the reduction of the chloride of silver 
by pure zinc. For this purpose suspend the chloride of silver 
by water, add hydrochloric acid, and place pure zinc rods or 
granulated zinc in the fluid. While zinc dissolves, metallic- 
silver is separated, which is filtered off, washed and dried. 



CHAPTER IX. 



DEPOSITION OF GOLD. 



Gold (Au = 197.2 parts by weight) is generally found in 
the metallic state. It is one of the metals possessing a yellow 
color. Precipitated from its solution with green vitriol (fer- 
rous sulphate) or oxalic acid, it appears as a brown powder 
without luster, which on pressing with the burnisher acquires 
the color and luster of fused gold. Pure gold is nearly as soft 
as lead, but possesses considerable tenacity. In order to in- 
crease the hardness when used for articles of jewelry and for 
coinage, it is alloyed with silver or copper. The "fineness of' 
gold," or its proportion in the alloy, is usually expressed by 
stating the number of carats present in 24 carats of the mix- 
ture. Pure gold is stated to be 24 carats "fine; " standard 
gold is 22 carats fine; 18 carat gold is a mixture of 18 parts 
of gold and 6 of alloy. Gold is the most malleable and duc- 
tile of the metals. It may be beaten out into leaves not ex- 
ceeding To;Voo °f a millimeter in thickness. When beaten 
out into thin leaves and viewed by transmitted light, gold 
appears green; when very finely divided it is dark red or 
black. The specific gravity of fused gold is 19.35, and that 
of precipitated gold powder, from 19.8 to 20.2. Pure gold 
melts at about 2016° F., and in fusing exhibits a sea-green 
color. The melting-points of alloyed gold vary according to 
the degree of fineness. Thus, 23 carat gold melts at 2012° F.; 
22 carat at 2009° ; 20 carat at 2002° ; 18 carat at 1995° ; 15 
carat at 1992°; 13 carat at 1990°; 12 carat at 1987°; 10 carat 
at 1982°; 9 carat at 1979°; 8 carat at 1973°; 7 carat at 
1960°. The fineness of gold may be approximately estimated 
by means of the touch-stone, a basaltic stone formerly obtained. 

(415) 



•416 ELECTRO-DEPOSITION OF METALS. 

from Asia Minor, but now procured from Saxony and 
Bohemia. The sample of gold to be tested is drawn across 
the stone, and the streak of metal is treated with dilute nitric 
acid. From the rapidity of the action and the intensity of 
the green color produced — due to the solution of the copper, as 
compared with streaks made by alloys of known composition 
— the assayer is enabled to judge of the proportion of inferior 
metal which is present. Gold preserves its luster in the air, 
and is not acted upon by any of the ordinary acids. Nitric, 
hydrochloric, or sulphuric acid by itself does not dissolve 
gold, but it dissolves in an acid mixture which develops 
chlorine, hence in aqua regia (nitro-hydrochloric acid). 

The gold found in commerce under the name of shell-gold 
or painter's gold, which is used in painting and for repairing 
smaller defects in electro-gilding, is prepared by triturating 
waste in the manufacture of leaf gold with water, diluted 
honey, or gum-water. Gold solution may also be precipitated 
with antimonic chloride. The resulting precipitate is tritu- 
rated with barium hydrate, extracted with hydrochloric acid, 
and after washing, the gold powder is triturated with gum 
arabic solution. 

Gold baths. Gold-plating may be effected in a hot or cold 
bath, large objects being generally plated in the latter, and 
smaller objects in the former. The hot bath has the advantage 
of requiring less current-strength, besides yielding deposits of 
greater density and uniformity, and of sadder, richer tones. 
Hot baths work with a moderate content of gold — 11 J to 12 J 
grains per quart of bath — while cold baths should contain not 
less than 54 grains per quart. 

Baths prepared with potassium ferrocyanide are preferred 
by some authors, while others work with a solution of gold 
salt and potassium bicarbonate, and others recommend a so- 
lution of cyanide of gold in potassium cyanide. With proper 
treatment of the bath, good results may be obtained with either. 
However, the use of baths prepared with potassium ferrocy- 
.anide cannot be recommended on account of the secondary 



DEPOSITION OF GOLD. 417 

■decompositions which take place during the operation of plat- 
ing, and because the baths do not dissolve the gold anodes. 
Below only approved formulas for the preparation of gold 
baths will be given. 

I. Bath for cold gilding. — Fine gold in the form of fulmi- 
nating gold 54 grains, 98 per cent, potassium cyandide 0.35 
to 0.5 oz. (according to the current-strength used), water 1 
•quart. 

Electro-motive force at 10 cm. electrode-distance, and with 
the use of 0.35 oz. of potassium cyanide, 1.35 volts ; with the 
-use of 0.5 oz. of potassium cyanide, 1.2 volts. 

Current-density, 0.15 amp&re. 

To prepare this bath, dissolve 54 grains of fine gold in aqua 
regia in a porcelain dish heated over a gas or alcohol flame, 
and evaporate the solution to dryness. Continue the heating 
until the solution is thickly-fluid and dark brown, and on 
cooling congeals to a dark brown mass. Heating too strongly 
should be avoided, as this would cause decomposition and the 
•auric chloride would be converted into aurous chloride, and 
•eventually into metallic gold and chlorine, which escapes. 
The neutral chloride of gold formed in this manner is dissolved 
in 1 pint of water and ammonia added to the solution so long 
•as a yellow-brown precipitate is formed, avoiding, however, 
•a considerable excess of ammonia. The precipitate of fulmi- 
nating gold is filtered off, washed, and dissolved in 1 quart 
•of water containing 0.5 oz. of potassium cyanide in solution. 
The solution is boiled, replacing the water lost by evaporation, 
until the odor of ammonia which is liberated by dissolving 
the fulminating gold in potassium cyanide disappears, when 
it is filtered. Instead of dissolving the gold and preparing 
neutral chloride of gold by evaporating, it is more convenient 
to use 108 grains of chemically pure neutral chloride of gold 
as furnished by chemical works, and precipitate the fulminat- 
ing gold from its solution. 

Too large an excess of potassium cyanide yields gold de- 
iposits of an ugly, pale color. When working with a more 
27 



418 ELECTRO-DEPOSITION OF METALS. 

powerful current, the excess of potassium cyanide need only 
be slight ; with a weaker current it may be larger. 

The fulminating gold must not be dried, as in this condi- 
tion it is highly explosive, but should be "immediately dis- 
solved while in a moist state. 

If the cost of a bath for cold gilding with such a high con- 
tent of gold as given in formula I should appear too great, 
only 27 grains of gold per quart may be used. With a suit- 
able electro-motive force, deposits of a beautiful, sad-yellow 
color are thus also obtained. Such a bath is yielded by the 
following formula : 

la. Fine gold in the form of neutral gold chloride 27 grains,. 
98 to 99 per cent, potassium cyanide 0.26 oz., water 1 quart. 

Electro-motive force at 10 cm. electrode-distance, 2.0 volts. 

Current-density, 0.15 ampere. 

For cold gilding, Roseleur recommends the following bath : 

II. Fine gold as neutral chloride of gold, 0.35 oz.; 98 per 
cent, potassium cyanide, 0.7 oz.; water, 1 quart. 

Electro-motive force at 10 cm. electrode-distance, about 1.5 
volts. 

Current-density, 0.12 ampere. 

Dissolve the gold-salt from 0.35 oz. of fine gold or about 
0.7 oz. of neutral chloride of gold in \ pint of the water, and 
the potassium cyanide in the other \ pint of water, and after 
mixing the solutions boil for half an hour. The preparation 
of this bath is more simple than that of formula I, but the 
color of the gold deposit obtained with the latter is warmer 
and sadder. The high content of gold in the bath, prepared 
according to formula II, readily causes a red-brown gold 
deposit, and hence special attention has to be paid to the 
regulation of the current. 

For those who prefer gold baths prepared with yellow prus- 
siate of potash instead of potassium cyanide, the following 
formula for cold-gilding is given : 

III. Yellow prussiate of potash (potassium ferrocyanide), 
0.5 oz.; carbonate of soda, 0.5 oz.; fine gold (as chloride of 
gold or fulminating gold), 30.75 grains; water, 1 quart. 



DEPOSITION OP GOLD. 419 

Electro-motive force at 10 cm. electrode-distance, 2 volts. 

Current-density, 0.15 ampere. 

To prepare the bath, heat the solutions of the yellow prus- 
siate of potash and of the carbonate of soda in the water to the 
boiling-point, add the gold-salt, and boil \ hour, or with use 
of freshly-precipitated fulminating gold, until the odor of am- 
monia disappears. After cooling, the solution is mixed with a 
quantity of distilled water, corresponding to the water lost by 
evaporation, and filtered. This bath gives a beautiful bright 
gilding upon all metals, even upon iron and steel. 

The yellow prussiate of potash baths are deservedly popular 
for decorative gilding, when gold deposits of different colors 
are to be produced upon an object. Certain portions have 
then to be covered with stopping-off varnish, the latter being 
less attacked by this bath than by one containing an excess 
of potassium cyanide. 

This bath is especially suitable for the so-called clock gild- 
ing. The articles are first provided with a heavy deposit of 
copper in the alkaline copper bath, then matt-coppered in the 
acid copper bath, next drawn through the bright-pickling 
bath, thoroughly rinsed, and finally gilded in the bath heated 
to about 122° F. 

Gold baths for hot gilding. — IV. Fine gold (as fulminating 
gold) 15.4 grains, 98 per cent, potassium cyanide 77 grains, 
water 1 quart. 

Electro-motive force at 10 cm. electrode-distance, 1.0 volt. 

Current-density, 0.1 ampere. 

This bath is prepared in the same manner as that according 
to formula I, from 15.4 grains of fine gold, which is converted 
into neutral chloride of gold by dissolving in aqua regia and 
evaporating ; or dissolve directly 29.32 to 30.75 grains of 
chemically pure neutral chloride of gold in water, precipitate 
the gold as fulminating gold with aqua ammonia, wash the 
precipitate, dissolve it in water containing the potassium cya- 
nide, and heat until the odor of ammonia disappears, replac- 
ing the water lost by evaporation. This bath yields a beau- 



420 ELECTRO-DEPOSITION OF METALS. 

tiful sad gilding of great warmth. All that has been said in 
regard to the content of potassium cyanide in the bath pre- 
pared according to formula I also applies to this bath. The 
temperature should be between 158° and 176° F., and the 
current-strength 2.0 to 2.5 volts. 

Roseleur recommends for hot gilding : 

V. Chemically pure crystallized sodium phosphate 2.11 ozs., 
neutral sodium sulphite 0.35 oz., potassium cyanide 30.86 
grains, fine gold (as chloride) 15.43 grains, distilled water 1 
quart. 

Electro-motive force at 10 cm. electrode distance 1.5 volts. 

Current-density, 0.12 ampere. 

If this bath is to serve for directly plating steel, only half 
the quantity of potassium cyanide is to be used, and the ob- 
jects should be covered with the use of a somewhat greater 
electro-motive force. Increasing the content of neutral sodium 
sulphite to 0.5 or 0.7 oz. also appears advisable. 

Dissolve in a porcelain dish, with the aid of moderate heat, 
the sodium phosphate and sodium sulphite, and when the 
solution is cold, add the neutral chloride of gold prepared 
from 15.43 grains of gold = about 30.86 grains of commercial 
chloride of gold, and the potassium cyanide. For use, heat 
the bath to between 158° and 167° F. 

For the preparation of gold baths for hot and cold gild- 
ing, double gold salts and triple gold salts, as well as gold 
solutions, as brought into commerce by some manufacturers 
may also be used. 

Many gold-platers prepare their gold baths with the assist- 
ance of the electric current. For this purpose prepare a solu- 
tion of 3.52 ozs. potassium cyanide (98 to 99 per cent.) per 
quart of water and, after heating to between 122° and 140° F., 
conduct the current of two Bunsen cells through two sheets of 
gold, not too small, which are suspended as electrodes in the 
potassium cyanide solution. The action of the current is 
interrupted when the solution is so far saturated with gold that 
an article immersed in it and connected to the negative pole 



DEPOSITION OF GOLD. 421 

in place of the other gold sheet, is gilded with a beautiful 
warm tone. By weighing the sheet of gold serving as anode, 
the amount of gold which has passed into the solution is 
ascertained. According to English authorities, a good gold 
bath prepared according to this method should contain 3.52 
ozs. of potassium cyanide and 0.7 oz. of fine gold per quart of 
water. 

The only advantage of this mode of preparing the bath is 
that it excludes a possible loss of gold, which may occur in 
dissolving gold, evaporating the gold solution, etc., by break- 
ing the vessel containing the solution. However, by using 
commercial chemically pure chloride of gold such loss is 
avoided, and the bath prepared according to the formulae 
given yields richer tones than a gold bath produced by electro- 
lysis. Besides, the preparation of the gold bath with the 
assistance of the electric current can only be considered for 
smaller baths, since the saturation of a larger volume of potas- 
sium cyanide solution requires considerable time, and- the 
potassium cyanide is strongly decomposed by long heating. 

Gold anodes. Management of gold baths. — It is advisable to 
keep the content of gold in the baths prepared according to 
the different formulae as constant as possible, which is best 
effected by the use of fine gold anodes. 

Insoluble platinum anodes are better liked in gilding than 
for all other electro-plating processes, partly because they are 
somewhat cheaper, and partly because they are recommended 
in most books on the subject. However, a bath which has 
become low in gold does not yield a beautiful gold color, and 
has to be frequently strengthened by the addition of chloride 
of gold or concentrated solution of fulminating gold in potas- 
sium cyanide, the preparation of which consumes time and 
causes expense, so that the use of gold anodes is the cheapest 
in the end, especially with the present high price of platinum. 

The use of steel anodes for cold and warm cyanide gold 
baths, advocated by some, cannot be recommended. Every 
gilder knows from experience that, when the enamel of the 



422 ELECTRO-DEPOSITION OF METALS. 

tanks containing the gold baths becomes defective, the baths 
in a short time fail. The reason for this is simply that the 
iron on the defective places of the tank decomposes the gold 
bath, metallic gold being reduced. Iron, in this respect, acts 
like zinc, which, in a still shorter time, precipitates metallic 
gold from gold baths. Now, when iron anodes remain sus- 
pended in the baths, a reduction of gold takes place, while a 
quantity of iron equivalent to the reduced gold is dissolved, 
and, in the form of ferric oxide, falls to the bottom of the vat. 

In hot gold baths this separation of gold proceeds still more 
rapidly and the content of potassium cyanide in the bath is 
destroyed, yellow prussiate of potash being formed. The 
argument made in favor of the use of steel anodes, that the 
old practitioners often added intentionally yellow prussiate of 
potash to their baths to heighten the gold tone is fallacious. 
A plater who works with gold baths prepared with yellow 
prussiate of potash cannot expect to replace the gold by the 
solution of the gold anodes, and when working with gold 
cyanide and potassium cyanide baths there is no inducement 
for gradually changing the bath into a yellow prussiate of 
potash bath by the use of steel anodes. 

According to one statement, a hot gold bath with steel 
anodes showed, after being electrolyzed for 70 hours, scarcely 
a trace of iron. To ascertain the correctness of this statement 
by an experiment, a gold bath prepared according to formula 
IV was electrolyzed at 158° F., with a blue annealed steel 
anode weighing 12.092 grammes. During the first two hours 
only a moderate yellow-reddish bloom of iron salt was per- 
ceptible on the anode, which became detached from the latter 
and fell to the bottom of the beaker. The bloom, however, 
became gradually heavier, the bottom of the beaker was 
covered with a precipitate of a yellow-brown color, the pre- 
viously colorless bath acquiring a yellow color and after elec- 
trolyzing for five hours, the blue color of the anode had largely 
■disappeared. The anode weighed now 11.832 grammes, and 
had consequently lost 2.2 per cent. After again suspending 



DEPOSITION OF GOLD. 423 

it in the bath it was more rapidly attacked in consequence of 
the destruction of the blue annealing color, which retarded 
corrosion. After five more hours the anode weighed 11.105 
grammes, the loss being therefore 8.16 per cent. The bath 
now showed a deep yellow color, and the precipitate on the 
bottom of the beaker had increased, while small, lighter flakes- 
of ferric hydrate spun around in the bath and attached them- 
selves to the anode. Electrolysis was now discontinued, since 
the last mentioned phenomena proved the uselessness of steel 
anodes for the reasons given under " Deposition of Nickel and 
Cobalt." 

As regards the advantage claimed for the use of steel 
anodes, that a large anode-surface corresponding to the object- 
surface can be rendered effective without taxing too severely 
the pocket-book of the gilder, it may be said that the same 
object can in a more rational manner be attained by employ- 
ing carbon anodes, which to prevent contamination of the 
bath by particles of carbon, are placed in linen bags. Crosses 
and balls of unusually large dimensions for church towers 
have frequently been gilded in Dr. Geo. Langbein & Co.'s 
establishment, for which a large anode-surface was required 
in order to obtain a uniformly heavy deposit, and in such 
cases carbon anodes of the best quality of retort graphite were 
used. These anodes, to be sure, become saturated with gold 
bath, and for that reason cannot be used for other baths. 
When not required for some time, they are kept in a vessel 
filled with clean water, and the latter is added to the bath to 
replace that lost by evaporation. 

The employment as anodes of platinum strips or platinum 
■wire may, perhaps, be advocated for coloring the deposit, i. e., 
for the purpose of obtaining certain tones of color when gild- 
ing in the hot bath. By allowing the platinum anode to dip 
only slightly in the bath a pale gilding is obtained, because 
the current thereby becomes weaker ; by immersing the anode 
deeper the color becomes more yellow, and by immersing it 
entirely the tone becomes more reddish. 



424 ELECTRO-DEPOSITION OF METALS. 

However, instead of producing these effects of the current- 
strength by the anode, which requires the constant presence of 
the operator, it is better to obtain the coloration by means of 
the rheostat. By placing the switch upon " strong," a reddish- 
gold tone is obtained, and by placing it upon " weak," a paler- 
gold tone, while the beautiful gold-yellow lies in the middle- 
between the two extremes. However, since even with the use- 
of gold anodes the content of gold in the bath is not entirely 
restored, the bath has after some time to be strengthened,, 
.which is effected by a solution of fulminating gold or chloride 
of gold in potassium cyanide, according to the composition of" 
the bath. 

The excess of potassium cyanide must not be too large, 
otherwise the gilding will be pale ; but, on the other hand, it 
must not be too small, since in this case quite a strong current 
would have to be used to effect a normal deposition of gold, 
which, besides, would not be dense and homogeneous. Too- 
small a content of potassium cyanide is indicated by the gold 
anodes showing dark streaks. 

As in the silvering baths, the excess of potassium cyanide- 
in the gold baths is also partially converted into potassium 
carbonate by the action of air, heat, etc., and it is, therefore,, 
advisable from time to time to add a small quantity of potas- 
sium cyanide. 

The presence of larger quantities of organic substances- 
which may get into the bath by dust or some other way, 
shows itself, as a rule, by a brownish coloration. Such baths- 
rarely yield a beautiful gold color, but deposit gold of a dark, 
tone. 

Unsightly and spotted deposits are also caused by a con- 
tamination of gold baths with compounds of lime which reach 
the bath by the use of water containing much lime, or by- 
insufficient removal of lime paste after freeing the objects from 
grease. 

Tanks for gold baths. Gold baths for cold gilding are kept 
in tanks of stoneware or enameled iron, or small baths in 



DEPOSITION OP GOLD. 



425^ 



glass tanks, which, to protect them against breaking, are placed 
in a wooden box. Baths for hot gilding require enameled 
iron tanks in which they can be heated by a direct fire, or 
better, by placing in hot water (water bath), or by steam. For 
small gold baths for hot gilding, a porcelain dish resting 
upon a short-legged iron tripod may be used (Fig. 129). Be- 
neath the iron tripod is a gas burner supplied with gas by 
means of a flexible India-rubber tube connected to an ordinary 
gas burner. Across the porcelain dish are placed two glass 
rods, around which the pole-wires are wrapped. 

In heating larger baths in enameled tanks over a direct; 

Fig. 129. 




fire it may happen that on the places most exposed to the 
heat the enamel may blister and peel off; it is, however,, 
better to heat the baths in a water or steam bath. For this 
purpose have made a box of stout iron or zinc sheet about 
| inch wider and longer, and about 4 inches deeper than the 
enameled tank containing the gold bath. To keep the level 
of the water constant, the box is to be provided with a water 
inlet- and overflow-pipe. In this box place the tank so that 
its edges rest upon those of the box, and make the joints tight 
with tow. The water-bath is then heated over a gas flame or 



.426 ELECTRO-DEPOSITION OF METALS. 

upon a hearth, the water lost by evaporation being constantly 
replaced, so that the enameled tank is always to half its 
height surrounded by hot water. For heating by steam the 
arrangement is the same, only a valve for the introduction, 
and a pipe for the discharge, of steam, are substituted for the 
water inlet- and overflow-pipe. 

Execution of gold-plating. — Most suitable current-density, 
0.15 to 0.2 ampere. Like all other electro-plating operations, 
it is advisable to effect gold-plating with an external source of 
current, that is, to use a battery or other source of current 
separated from the bath, and to couple the apparatuses as pre- 
viously described and illustrated by Figs. 44 and 45. 

To be sure, there are still gilders who gild without a battery 
or separate external source of current and obtain good results, 
the process being, as a rule, employed only in gilding small 
articles. The apparatus used for this purpose consists of a 
glass vessel containing the gold solution compounded with a 
large excess of potassium cyanide, and a porous clay cup filled 
with very dilute sulphuric acid or common salt solution, which 
is placed in the glass vessel. Care should be taken to have 
the fluids in both vessels at the same level. Immerse in the 
clay cup an amalgamated zinc cylinder or zinc plate, to which 
a copper wire is soldered. Outside the cup this copper wire is 
bent downwards, and the article to be gilded, which dips in 
the gold solution, is fastened to it. In working with this ap- 
paratus there is always a loss of gold, since the gold solution 
penetrates through the porous cup, and on coming in contact 
with the zinc is reduced by it, the gold being separated as 
black powder upon the zinc. In cleaning the apparatus this 
black slime has to be carefully collected and worked for fine 
gold. 

For the sake of greater solidity, only articles of silver and 
copper and its alloys should be directly gilded, while all other 
metals are best first brassed or coppered. Cleaning from grease 
and pickling is done in the same manner, as described on page 
228. The preparation of the articles for gilding differs from 



DEPOSITION OF GOLD. 427 

that for silvering only in that the surfaces, which later on are 
to appear with high luster, are not artificially roughened with 
emery, pumice, or by pickling, because, on the one hand, the 
gold deposit seldom needs to be made extravagantly heavy, 
and the rough surface formed would require more laborious 
polishing with the burnishers ; and, on the other, the gold de- 
posits adhere quite well to highly-polished surfaces, provided 
the current-strength is correctly regulated, and the bath 
accurately composed according to one of the formulas given. 
Quicking the articles before gilding, which is recommended 
by some authors, is not necessary. 

The current-strength must, under no circumstances, be so 
great that a decomposition of water, and consequent evolution 
of hydrogen on the objects, takes place, since otherwise the 
gold would not deposit in a reguline and coherent form, but as 
a brown powder. By regulating the current-strength so that 
it just suffices for the decomposition of the bath, and avoiding 
a considerable surplus, a very dense and uniform deposit is 
formed ; and by allowing the object to remain long enough in 
the bath, a beautiful, mat gold deposit can be obtained in all 
the baths prepared according to the formulas given. It may, 
however, be mentioned that this mode of mat gilding is the 
most expensive, since it requires a very heavy deposit, and it 
will, therefore, be better to matten the surface previous to 
gilding, according to a process to be described later on. 

Constant agitation of the objects in the baths, or of the lat- 
ter itself, is of great advantage for obtaining good gilding. It 
is evident that by reason of the small amount of metal in the 
gold baths, especially in warm ones, the strata of fluid on the 
cathodes become rapidly poor in metal, and if care be not 
taken to replace them by strata of fluid richer in gold, dis- 
turbances in deposition will result. 

For gilding with cold baths, two freshly-filled Bunsen cells 
coupled for electro-motive force suffice in almost all cases, 
while for hot baths one cell is, as a rule, sufficient, if the 
anode surface is not too small. The more electro-positive the 
metal to be gilded is, the weaker the current can and must be. 



428 ELECTRO-DEPOSITION OF METALS. 

Though gold solutions are good conductors, and, therefore,. 
the portions of the articles which do not hang directly oppo- 
site the anodes gild well, for solid plating of larger objects it 
is recommended to frequently change their positions, except 
when they are entirely surrounded by anodes. 

The inner surfaces of hollow-ware, such as drinking-cups r 
milk pitchers, etc., are best plated after freeing them from 
grease and pickling, by filling the vessel with the gold bath 
and suspending a current-carrying gold anode in the center 
of the vessel, while the outer surface of the latter is brought 
in contact with the negative conducting w 7 ire. The lips of 
vessels are plated by placing upon them a cloth rag saturated 
with the gold bath and covering the rag with the gold anode. 

For gold-plating in the cold bath the process is as follows : 
The objects, thoroughly freed from grease and pickled (and if 
of iron, zinc, tin, Britannia, etc., previously coppered), are 
suspended in the bath by copper wires, where they remain 
with a weak current until in about 8 or 10 minutes they ap- 
pear uniformly plated. At this stage they are taken from the 
bath, rinsed, in a pot filled with water, and the latter, after- 
having been used for some time, is added to the bath to re- ■ 
place the water lost by evaporation. The articles are finally 
brushed with a fine brass scratch-brush and tartar solution,, 
thoroughly rinsed, again freed from grease by brushing with 
lime-paste and then returned to the bath, where they remain 
until they have acquired a deposit of sufficient thickness. 

When an article is to have a very heavy deposit, it is ad- 
visable to scratch-brush it several times with the use of tartar 
or its solution, or with a solution of size and water, between 
the intermediate coats of gold. By these means a very durable- 
and lasting coating of gold will be secured. For gold plating 
by weight the same plan as given for silver-plating by weight 
(p. 382) is pursued. 

For gold-plating with the hot bath, the operations are the 
same, with the exception that a weaker current is introduced 1 
into the bath and the time of the plating process shortened- 



DEPOSITION OP GOLD. 429 

Frequent scratch-brushing also increases the solidity of the 
•deposit and prevents its prematurely turning to a dead brown- 
black. Since in hot plating more gold than intended is 
readily deposited; it is especially advisable to place a rheostat 
and voltmeter in the circuit, as otherwise the operator must 
remain standing along-side of the bath and regulate the effect 
of the current by immersing the anodes more or less. 

When taken from the bath, the finished gilded objects should 
show a deep yellow tone, which, after polishing, yields a full 
gold color. If the objects come from the bath with a pale 
gold tone, the deposit, after polishing, shows a meager, pale 
gold color, which is without effect. Gold deposits of a dark 
or brown color also do not yield a sad gold tone. 

With a somewhat considerable excess of potassium cyanide, 
and if the objects to be plated are not rapidly brought in con- 
tact with the current-carrying object rod, hot gold baths cause 
the solution of some metal. Therefore when silver or silver- 
plated objects are constantly plated in them they yield a some- 
what greenish gilding in consequence of the absorption of 
silver, or a reddish gilding due to the absorption of copper, if 
copper or coppered articles are constantly plated in them. 
Hence, for the production of such green or reddish color, 
gold-plating baths which have thus become argentiferous or 
cupriferous, may be advantageously used. In order to obtain 
a deposit of green or red gold with fresh baths, the tone-giving 
addition of metal must be artificially effected, as will pres- 
ently be seen. 

If, however, such extreme tones are not desired, the content 
of gold in the baths may be exhausted for preliminary plat- 
ing with the use of platinum anodes, the sad gold color being 
then given in a freshly prepared bath. 

The gold deposits are polished in the same manner as silver 
deposits, with the burnisher and red ochre, and moistening 
with solution of soap, decoction of flaxseed, or soap-root, etc. 
For less heavy gilding the articles, previous to gilding, are 
given high luster, and after gilding, burnished with rouge 
and buckskin. 



430 ELECTRO-DEPOSITION OF METALS. 

Red-gilding. In order to obtain a red gold with the formulas 
given, a certain addition of copper cyanide dissolved in potas- 
sium cyanide has to be made to them. The quantity of such 
addition cannot be well expressed by figures, since the current 
strength with which the articles are plated exerts considerable 
influence. It is best to triturate the copper cyanide in a mor- 
tar to a paste with water, and add of this paste to a moderately 
concentrated potassium cyanide solution as long as copper 
cyanide is dissolved. Of this copper solution add, gradually 
and in not too large portions, to the gold solution until, with 
the current-strength used, the gold deposit shows the desired 
red tone, and if fine gold anodes are used, the bath is kept 
constant with this content of copper by an occasional addition 
of the above-mentioned copper solution. 

The absorption of copper in the bath may also be effected 
by suspending, in place of gold anodes, anodes of copper or 
copper-gold alloys, for instance, fourteen-carat gold, and allow- 
ing the current to circulate (suspension of a few gold anodes 
to the object-rod). The direct addition of copper cyanide, 
however, deserves the preference. 

In place of preparing the solution of copper cyanide in 
potassium cyanide, commercial crystallized potassium-copper 
cyanide may be used. It is dissolved in warm water, and of 
the solution a sufficient quantity is gradually added to the 
gold bath. 

For the determination of the content of copper required for 
the purpose of obtaining a beautiful red gold, a bath for hot 
gilding which contained 10.8 grains of gold per quart was 
compounded with a solution of copper cyanide in potassium 
cyanide with 1.08 grains content of copper. The tone of the 
gilding, which previously was pure yellow, immediately passed 
into a pale red gold. By the further addition of 1.08 grains 
of copper, a fiery red gold tone was obtained, while a third 
addition of 1.08 grains of copper yielded a color more ap- 
proaching that of copper than of gold. These experiments 
show that 20 per cent, of copper of the weight of gold con- 



DEPOSITION OF GOLD. 431 

tained in the bath seems to be the most suitable proportion 
for obtaining a beautiful red gold. 

Rings, watch-chains and other objects of base metal are fre- 
quently to be plated with red gold, so as to show no percepti- 
ble sign of having been attacked by nitric acid, even after re- 
maining in it for several hours. This may be effected by first 
giving the objects a deposit of a strongly yellow color by gild- 
ing in a bath containing 10.8 to 15.43 grains of gold per quart 
and then coloring them in the red gilding bath. This process 
may be called an imitation of mechanical gold plating, and is 
frequently made use of in the jewelry industry. 

A method of gilding chains and other articles manufac- 
tured from common metal, in imitation of genuine gold 
articles is given by Gee as follows : A bath is prepared by 
dissolving a quantity of pure gold and making a solution of 
it in the usual manner, and then using a large copper anode 
instead of a gold one in the process of gilding. 

The articles are gilt until they stand the acid test, when 
they are well burnished until they present a bright gold-like 
appearance. If the articles are slightly gilt as a first process 
and then burnished, and afterwards more thickly gilt and 
again burnished, much less gold is required than if the pro- 
cess is conducted straight to the end without any inter- 
mediate burnishing. The burnishing stops up all the pores 
of the metal by the adoption of this plan, and more quickly 
renders the articles gilt acid proof and that at the expense of 
much less gold. When the solution begins to gild of an in- 
ferior color it is abandoned and another one made. It pro- 
duces a surface alloy of about 16 or 18 carat, and well answers 
the purpose for which it has been designed. 

Green gilding. To obtain greenish gilding, solution of 
cyanide or chloride of silver in potassium cyanide has to be 
added to the gold bath. It is not easy to prepare greenish 
gilding of a pleasing color, and to obtain it the current-strength 
must be accurately proportioned to the object-surface, since 
with too weak a current silver predominates in the deposit, 



432 ELECTRO-DEPOSITION OF METALS. 

the gilding then turning out whitish, while too strong a cur- 
rent deposits too much gold in proportion to silver, the gilding 
becoming yellow, but not green. 

Rose-color gilding may be obtained by the addition of suit- 
able quantities of copper and silver solutions, but such colora- 
tion requires much attention and thought. 

Rose gold solution. — Probably one of the best solutions for 
the rose gold, sometimes also termed old gold is, according to 
Mr. Chas. H. Proctor,* made from \ oz. of pure 24-karat gold, 
dissolved in aqua regia in the usual manner, then precipitated 
as fulminate with ammonia (26°), and then well washed. 
Add the gold salt to a solution of 1 gallon of cyanide solution, 
standing 2 to 3° Be, and add J oz. of hyposulphite of sodium 
to each gallon of solution so prepared. This solution will 
produce a good flash gold with a weak current. Cheap rose 
gold work is first acid copper plated for a few minutes, then 
relieved on the high lights, and then gilded. Gold work is 
run for five to ten minutes with a strong current, according to 
the tone required, then relieved with sodium bicarbonate in- 
stead of pumice stone. 

To produce a rose gold finish without the use of gold a 
number of concerns are using the Electrochroma Process, in 
which the articles are immersed in a special bath in the same 
manner as employed in plating. In a minute or two the 
articles are coated with a pinkish yellow surface that resembles 
rose gold. The surface is afterwards relieved to produce a 
contrast effect on the high lights. 

This finish can also be imitated very successfully by the 
following method : All articles, except those of brass, should 
be previously brass-plated and then a surface similar to the 
brush brass finish produced. Use floated silax instead of 
pumice stone so that the surface will be even and not have a 
scratchy appearance. Then gold lacquer, using a yellowish 
instead of a red toned lacquer. The surface should be thor- 

* Metal Industry, June, 1913. 



DEPOSITION OF GOLD. 433 

oughly dried on the lacquer heater. The rose tone is then 
produced by mixing dry orange chrome and a very little 
finely powdered gold rouge, mixed with turpentine and a tea- 
spoonful of turpentine varnish per pint of the mixture. This 
should be mixed to a thinly fluid paint and then applied to 
the detail work with a soft brush. The articles should then 
be dried for a short time by the aid of heat and allowed to 
become cool. The surface should be opaque without any 
luster when dry. Now mix up equal parts of boiled linseed 
oil and turpentine and use this for reducing the color from the 
surface. To accomplish this operation, moisten soft rags with 
the mixture and remove the colors from the high lights or 
■detail work. After this is done the articles will have the ap- 
pearance of true rose gold. 

For the sake of completeness, a method of gilding which is 
a combination of fire-gilding with electro-deposition, may 
here be mentioned, though experiments made with it failed to 
show the advantages claimed for it, because it does not yield 
as dense a deposit as fire-gilding, nor can the volatilization of 
mercury be avoided, the latter operation being the most dan- 
gerous part of fire-gilding. 

According to Du Fresne, the process is as follows : 

The articles are first coated with mercu^, with the assist- 
ance of the current, in a mercurial solution consisting of 
cyanide of mercury in potassium cyanide, with additions of 
carbonate and phosphate of soda, then gilded in an ordinary 
gilding-bath, next again coated with mercury, then again 
gilded, and so on, until a deposit of sufficient thickness is 
obtained. The mercury is then evaporated over glowing 
coals, and the articles, after scratch-brushing, are burnished. 

According to another process, the articles are gilded in a bath, 
■consisting of 98 per cent, potassium cyanide 1.2 ozs., cyanide 
of gold 92| grains, cyanide of mercury 22| grains, distilled 
water 1 quart, a strong current being used. When the objects 
are sufficiently gilded, the mercury is evaporated in the above- 
mentioned manner, and the objects are scratch-brushed, and 
finally polished. 
28 



434 ELECTRO-DEPOSITION OF METALS. 

Mat gilding. — As previously mentioned, a beautiful mat 
gold deposit may be obtained by the use of any of the for- 
mulas given, and a current correctly regulated, and allowing 
sufficient time for gilding. The heavy deposit of gold required 
for this process makes it, however, too expensive, and it is, 
therefore, advisable to produce mat gilding by previously 
matting the basis-surface, since then a thinner deposit of gold, 
will answer very well. The process of graining will be 
referred to later on under " Silvering by Contact/' etc. 

Another method is to mat the first slight deposit by means 
of brass or steel-wire brushes, and then to give a second de- 
posit of gold, which also turns out mat upon the matted 
surface. The character of the mat produced depends on the 
thickness of the wire of the brushes. Thicker wire gives a 
mat of a coarser grainy and thinner wire one of a finer grain. 

Objects may be readily matted with the use of the sand 
blast, after which they are quickly drawn through the bright 
dipping bath, thoroughly rinsed, and brought into the gold; 
bath. 

Matting by chemical or electro- chemical means is effected by- 
one of the following methods : 

For this purpose the mixture of 1 volume of saturated solu- 
tion of bichromate of potash and 2 volumes of concentrated 
hydrochloric acid, mentioned on p. 225, may be used. Brass 
articles are allowed to remain several hours in the mixture, 
and are then quickly drawn through the bright-dipping bath.. 
Copper alloys might also be successfully matted by suspend- 
ing them as anodes in a mixture of 90 parts water and 10' 
parts sulphuric acid, and drawing the matted articles through 
the bright-dipping bath. 

Or, they are mat-silvered, and the gold is deposited upon 
the matted layer of silver. Articles gilded upon a mat silver 
basis, however, acquire before long an ugly appearance, since 
in an atmosphere containing sulphuretted hydrogen the silver 
turns black, even under the layer of gold and shines through. 

More advantageous is the process of providing the articles. 



DEPOSITION OF GOLD. 435 

with a mat copper coating in the acid galvanoplastic bath. 
They are then drawn through a not too strong pickle, rinsed, 
and gilded. This process is used for the so-called French 
clock gilding, and yields a very sad, beautiful gilding. The 
articles consisting of zinc are first heavily coppered in a cyanide 
copper bath, then matted in the acid copper bath (see " Gal- 
vanoplasty "), care being taken that the slinging wire is in 
contact with the object-rod, which conducts the current, be- 
fore the coppered zinc objects is suspended in the bath. This 
process of coppering zinc in the acid copper bath is, however, 
quite a delicate operation, and it will frequently be noticed, 
even with apparently very heavy coppering in the cyanide 
copper bath, that in suspending the articles in the acid bath, 
brownish-black places appear on which, by contact of the 
acid bath with zinc, copper in a pulverulent form is depos- 
ited. When this is observed, the articles must be immedi- 
ately taken from the bath, thoroughly scratch-brushed, and 
again thoroughly and heavily coppered in the cyanide copper 
bath, before replacing them in the acid copper bath. It may 
be recommended to provide the coppered zinc articles with a 
thick deposit of nickel, and then to copper them mat in the 
acid bath, the percentage of unsuccessful coppering being 
much smaller than without previous nickeling. The mat- 
coppered articles are rapidly drawn through the bright-dipping 
bath and then gilded, the bath prepared according to formula 
III, and heated to about 140° F., being very suitable for the 
purpose. 

Coloring of the gilding. It has been repeatedly mentioned 
that the most rational and simple process of giving certain 
tones of color to the gilding is by means of a stronger or 
weaker current. Many operators, however, cling to the old 
method of effecting the coloration by gilder's wax or brushing 
with certain mixtures, and for this reason this process, which 
is generally used for coloring fire-gilding, shall be briefly 
mentioned. 

To impart to the gold-deposit a redder color, the gilding-wax 



436 ELECTRO-DEPOSITION OP METALS. 

is prepared with a greater content of copper, while for greenish 
gilding more zinc-salt is added. There are innumerable re- 
ceipts for the preparation of gilding wax, nearly every gilder 
having his own receipt, which he considers superior to all 
others. Only two formulas which yield good results will have 
to be given one (I) for reddish gilding and one (II) for greenish 
gilding. 

I. Wax 12 parts by weight, pulverized verdigris 8, pulver- 
ized sulphate of zinc 4, copper scales 4, borax 1, pulverized 
bloodstone 6, copperas 2. 

II. Wax 12 parts by weight, pulverized verdigris 4, pulver- 
ized sulphate of zinc 8, copper scales 2, borax 4, pulverized 
bloodstone 6, copperas 2. 

Gilder's wax is prepared as follows : Melt the wax in an 
iron kettle, add to the melted mass, while constantly stirring, 
the other ingredients, pulverized and intimately mixed, in 
small portions, and stir until cold, so that the powder cannot 
settle on the bottom or form lumps. Finally, mould the soft 
mass into sticks about J inch in diameter. 

Gilder's wax is applied as follows: Coat- the heated gilded 
articles uniformly with the wax, and burn off over a charcoal 
fire, frequently turning the articles. After the wax flame is 
extinguished, plunge the articles into water, scratch-brush 
with wine-vinegar, dry in sawdust, and polish. 

To give gilded articles a beautiful, rich appearance, the fol- 
lowing process may also be used : Mix 3 parts by weight of 
pulverized alum, 6 of saltpetre, 3 of sulphate of zinc, and 3 of 
common salt, with sufficient water to form a thinly-fluid 
paste. Apply this paste as uniformly as possible to the articles 
by means of a brush, and after drying, heat the coating upon 
an iron plate until it turns black ; then wash in water, 
scratch-brush with wine-vinegar, dry and polish. 

According to a French receipt, the same result is attained by 
mixing pulverized blue vitriol 3 parts by weight, verdigris 7, 
ammonium chloride 6, and saltpetre 6, with acetic acid 31 ; 
immersing the gilded articles in the mixture, or applying the 



DEPOSITION OP GOLD. 437 

latter with a brush ; then heating the objects upon a hot iron 
plate until they turn black, and, after cooling, pickling in 
concentrated sulphuric acid. 

Some gilders improve bad tones of gilding by immersing the 
articles in dilute solution of nitrate of mercury until the gild- 
ing appears white. The mercury is then evaporated over a 
flame and the articles are scratch-brushed. Others apply a 
paste of pulverized borax and water, heat until the borax 
melts, and then quickly immerse in dilute sulphuric acid. 

Incrustations with gold are produced in the same manner as 
incrustations with silver, described on p. 403. 

Gilding of metallic wire and gauze. — Fine wire of gilded 
copper and brass is much used in the manufacture of metallic 
fringes and lace, for epaulettes and other purposes. The fine 
copper and brass wires being drawn through the draw-irons 
and wound upon spools by special machines, and hence not 
touched by the hands, freeing from grease may, as, a rule, be 
omitted. The first requisite for gilding is a good winding 
machine, which draws the wires through the gold bath and 
wash-boxes, and further effects the winding of the wire upon 
spools. The principal demand made in the construction of 
such a machine is that by means of a simple manipulation a 
great variation in the speed with which the wire or gauze 
passes through the gold bath can be obtained. This is neces- 
sary in order to be able to regulate the thickness of the gilding 
by the quicker or slower passage of the wire. A machine well 
adapted for this purpose is that constructed by J. W. Spaeth, 
and shown in Fig. 130. 

The variation in the passage of the wire is attained by the 
two friction-pulleys F, which sit upon a common shaft with 
the driving pulley R, and transmit their velocity by means of 
the friction-pistons KK' to the friction-pulley F f , which is 
firmly connected to the belt-pulley R driving the spool spindle- 
Since by a simple device the pistons i^and K' may be shifted, 
it is clear that the transmission of the number of revolutions 
from F to F' is dependent on the position of the friction- 



438 



ELECTRO-DEPOSITION OF METALS. 



pistons K and K', and that the velocity will be the greater 
the shorter the distance they are from the center of friction- 
pulleys .Fand F. In order that the friction between F, K 
.-and F' may always be sufficient for the transmission of the 
motion, even when the pistons are worn, four weights, G, are 
provided, which press the above-mentioned parts firmly against 
each other. 

In front of each spool of this machine is inserted a small 



Fig. 130. 




enameled iron tank which contains the gold bath, and is 
heated by a gas flame to about 167° F. Between this bath 
and the winding machine is another small tank with hot 
water in which the gilded wire is rinsed. 

The wire unwinds, from a reel placed in front of the gold 
baths, runs over a brass drum which is connected to the nega- 
tive pole of the source of current and transmits the current to 
the wire. The dipping of the wire into the gold bath is 
effected by porcelain drums, which are secured to heavy 
pieces of lead placed across the tanks, as shown in Fig. 131. 
The gilded wire being wound upon the spools of the winding 



DEPOSITION OF GOLD. 439 

machine, these spools are removed and thoroughly dried in 
the drying chamber. The wire is then again reeled off onto 
•a simple reel, in doing which it is best to pass it through be- 
tween two soft pieces of leather to increase its luster. 

For gilding wire the most suitable gold bath is that pre- 
pared according to formula IV. The electro-motive force 
should be from 6 to 8 volts, in order to produce a deposit of 
sufficient thickness, even when the wire passes at the most 
rapid rate through the bath. For this reason a dynamo with 
■a voltage of 10 volts is almost exclusively used for wire gild- 
ing. 

As a rule an anode of platinum — a strip of platinum sheet 
— of the same length as the tank is placed upon the bottom 
•of the latter, and connected by means of platinum wire to the 
positive pole of the source of current. The use of gold anodes 

Fig. 131. 



S^ 



for wire gilding is not required, since the small gold baths — 
generally only 2 to 4 quarts — are as far as possible to be 
worked till exhausted, when they are replaced by fresh baths. 

In place of platinum anodes, Stockmeir recommends the 
use of blued Bessemer steel anodes for wire gilding. In this 
■case there can be no objection to steel anodes, because the 
baths are rapidly exhausted, and then go amongst the gold- 
residues. But, nevertheless, the use of an indestructible plati- 
num anode would appear to deserve the preference, the baths 
being without doubt kept cleaner than with steel anodes. 

Silver-plated wires are, as a rule, to be gilded, and since the 
color of the basis-metal exerts an influence upon the gilding, 
Stockheimer recommends brassing the silver-plated or solid 
silver wires previous to gilding, because a gold-deposit of less 



440 ELECTRO-DEPOSITION OF METALS. 

thickness than for covering the white silver, would thus be- 
required. The proposition to gild nickeled wires, in place of 
silver-plated wires, because they are less subject to rapid dis- 
coloration in an atmosphere containing sulphuretted hydro- 
gen, also deserves consideration. 

Stripping gold from gilded articles. — Gilded articles of iron 
and steel are best stripped by treating them as anodes in a 
solution of from 2 and 2f ozs. of 98 per cent, potassium cyan- 
ide in 1 quart of water, and suspending a copper plate greased 
with oil or tallow as the cathode. Gilded silverware is readily 
stripped by heating to ignition, and then immersing in dilute 
sulphuric acid, whereby the layer of gold cracks off, the heat- 
ing and subsequent immersion in dilute sulphuric acid being 
repeated until all the gold is removed. Before heating and 
immersing in dilute sulphuric acid, the articles may first be 
provided with a coating of a paste of ammonia chloride, 
flowers of sulphur, borax and nitrate of potash which is allowed 
to dry. On the bottom of the vessel containing the dilute 
sulphuric acid, the gold will be found in laminae and scales, 
which are boiled with pure sulphuric acid, washed and finally 
dissolved in aqua regia, and made into chloride of gold or 
fulminating gold. 

To strip articles of silver, copper or German silver which will 
not bear heating, the solution of gold may be effected in a 
mixture of 1 lb. of fuming sulphuric acid, 2.64 ozs. of con- 
centrated hydrochloric acid, and 1.3 ozs. of nitric acid of 40° 
Be. Dip the articles in the warm acid mixture, and observe 
the progressive action of the mixture by frequently removing 
the articles from it. The articles to be treated must be per- 
fectly dry before immersing in the acid mixture, and care 
must be had to preserve the latter from dilution with water in 
order to prevent the acids from acting upon the basis-metal. 

The process by which scratched or rubbed rings are, so to 
say, electrolytically smoothed and polished, may be called a 
sort of stripping. For this purpose the rings are suspended as 
anodes in a bath consisting of: Water 1 quart, yellow prussiate 



DEPOSITION OF GOLD. 441 

of potash 1 oz., 99 per cent, potassium cyanide T \ ozs. By 
conducting a current of high electro-motive force, of about 20 
to 25 volts, through the bath any roughness or unevenness is 
in a few minutes removed, and the rings will be almost per- 
fectly smooth when taken from the bath. A sheet of gold or 
platinum is used as cathode. 

Determination of genuine gilding. — Objects apparent gilded 
are rubbed upon the touchstone, and the streak obtained is 
treated with pure nitric acid of 1.30 to 1.35 specific gravity. 
The metal contained in the streak thereby dissolves, and as far 
as it is not gold, disappears, while the gold remains behind. 
The stone should be thoroughly cleansed before each operation 3 - 
and the streak should be made, not with an edge or a corner 
of the object to be tested, but with a broader surface. If no- 
gold remains upon the stone, but there is nevertheless, a sus- 
picion of the article being slightly gilded, proceed with small 
nrlicles as follows: Take hold of the article with a pair of 
tweezers, and after washing it first with alcohol, and then with 
ether, and drying upon blotting paper, pour over it in a test, 
glass, cleansed with alcohol or ether, according to the weight 
of the article, 0.084 to 5.64 drachms of nitric acid of 1.30 spe- 
cific gravity free from chlorine. The article will be immedi- 
ately dissolved, and if it has been gilded never so slightly, per- 
ceptible gold spangles will remain upon the bottom of the 
glass. 

Examination of Gold Baths. 

The determination of free potassium cyanide and of the 
polassium carbonate which is formed, is effected in the same 
manner as given under " Examination of copper baths and 
of silver baths." 

The determination of the gold is effected by the electrolytic- 
method. With baths poor in gold, 50 cubic centimeters are 
used for electrolysis, and with baths rich in gold, 25 cubic- 
centimeters". After diluting with water to within 1 centimeter 
of the rim of the platinum dish, the liquid is electrolyzed for. 



442 ELECTRO-DEPOSITION OF METALS. 

about three hours with a current-density ND 100 = 0.067 
ampere, the complete separation of the gold being recognized 
by a platinum strip suspended over the rim of the dish and 
dipping into the fluid showing in fifteen minutes no trace of 
a separation of gold. 

The dish is then washed, rinsed with alcohol, and dried at 
212° F. To obtain the content of gold in grammes per liter of 
bath, multiply the weight of the precipitate by 20, when 50 
cubic centimeters, or by 40, when 25 cubic centimeters, of the 
bath have been used. 

The content of gold in the baths declines constantly, es- 
pecially with the use of platinum and carbon anodes. For 
strengthening the bath neutral gold chloride dissolved in 
potassium cyanide is used, 2 grammes neutral gold chloride 
and 1.4 grammes 99 per cent, potassium c} 7 anide dissolved in 
a small quantity of water or directly in the bath, being re- 
quired for every gramme of gold deficit in the baths. 

The determination of gold described above is suitable only 
for baths prepared with potassium cyanide, which contain the 
gold in the form of potassium-gold cyanide. The determina- 
tion of gold in baths prepared with yellow prussiate of potash 
is more difficult and should be made by a skilled anatyst. 

Recovery of gold from gold baths, etc. To recover the gold 
from old C3 7 anide gilding baths, evaporate the baths to dry- 
ness, mix the residue with litharge, and fuse the mixture. 
The gold is contained in the lead button thus obtained. The 
latter is then dissolved in nitric acid, whereby the gold re- 
mains behind in the form of spangles. These spangles are 
filtered off and dissolved in aqua regia. 

The recovery of gold from gold baths ma} r also be advan- 
tageously effected by precipitation with zinc dust according 
to the same process as given for the recovery of silver, p. 413. 
After removing the zinc by means of hydrochloric acid and 
washing the gold powder, the latter is dissolved in aqua regia 
-and the chloride of gold solution evaporated to dryness. 
-Aluminium powder is still more suitable for precipitating the 



DEPOSITION OF GOLD. 443 

gold ; the excess of aluminium is dissolved by potash or 
soda lye. 

From the acid mixtures serving for mat pickling gold, or 
for stripping, the gold is precipitated by solution of sulphate 
of iron (copperas) added in excess. The gold present is pre- 
cipitated as a brown powder mixed with ferric oxide. This 
powder is filtered off and treated in a porcelain dish with hot 
hydrochloric acid, which dissolves the iron. The gold which 
remains behind is then filtered off, and, after washing, dis- 
solved in aqua regia in order to work the solution into ful- 
minating gold or neutral chloride of gold. 

For gilding by contact, boiling and friction, see special chap- 
ter "Deposition by Contact." 



CHAPTER X. 

DEPOSITION OF PLATINUM AND PALLADIUM. 
1. Deposition of Platinum (Pt = 195.2 Parts by Weight). 

Properties of platinum. — Pure platinum is white with a gray- 
ish tinge. It is as soft as copper, malleable and very ductile. 
At a white heat it can be welded, but is fusible only with the 
oxyhydrogen blowpipe or by the electric current. Its specific 
gravity is 21.4. 

Air has no oxidizing action upon platinum. It is scarcely 
acted upon by any single acid ; prolonged boiling with con- 
centrated sulphuric acid appears to dissolve the metal slowty. 
The best solvent for it is aqua regia, which forms the tetra- 
chloride, PtCl 4 . Chlorine, bromine, sulphur and phosphorus 
combine directty with platinum', and fusing saltpetre and 
caustic alkali attack it. 

Besides, in the malleable and fused state, platinum may be 
obtained as a very finely divided powder, the so-called plati- 
num black, which is precipitated with zinc from dilute solution 
of platinum chloride acidulated with hydrochloric acid. 

Platinum baths. — In view of the valuable properties of plat- 
inum of oxidizing only under certain difficult conditions, of 
possessing an agreeable white color, and of taking a fine 
polish, it seems strange that greater attention has not been 
paid to the electro-deposition of this metal than is actually 
the case. The reason for this may perhaps be found in the 
fact that the baths formerty employed for experiments pos- 
sessed serious defects, causing the operator many difficulties r 
and besides, allowed only of the production of thin deposits. 
Giving due consideration to the requirements of the process 
of electro-deposition of platinum, and with the use of a suit- 

(444) 



DEPOSITION OF PLATINUM AND PALLADIUM. 445 

able bath, deposits of platinum of a certain thickness can be 
readily produced, and necessary conditions will be described 
under "Treatment of Platinum Baths." 

The platinum baths formerly proposed did not yield satis- 
factory results, because the content of platinum was too small 
in some of them, while with others dense deposits could not be 
obtained. A more recent formula by Bottger, however, gives 
quite a good bath. A moderately dilute, boiling-hot solution 
of sodium citrate is added to platoso-ammonium chloride until 
an excess of the latter no longer dissolves, even after continued 
boiling. The following proportions have been found very 
suitable : Dissolve 17J ozs. of citric acid in 2 quarts of water, 
and neutralize with caustic soda. To the boiling solution add, 
whilst constantly stirring, the platoso-ammonium chloride 
freshly precipitated from 2.64 ozs. of chloride of platinum, 
heat until solution is complete, allow to cool, and dilute with 
water to 5 quarts. To decrease the resistance of the bath, 0.7 
or 0.8 oz. of ammonium chloride may be added ; a larger 
addition, however, will cause the separation of dark-colored 
platinum. 

The platoso-ammonium chloride is prepared by adding to a 
concentrated solution of platinic chloride, concentrated solu- 
tion of ammonium chloride until a yellow precipitate is no 
longer formed on adding a further drop. The precipitate is 
filtered off and brought into the boiling solution of sodium 
citrate. The bath works very uniformly if the content of 
platinum is from time to time replenished. 

" The Bright Platinum Plating Company," of London, has 
patented the following composition of a platinum bath : Chlor- 
ide of platinum 0.98 oz., sodium phosphate 19f ozs., ammo- 
nium phosphate 3.05 ozs., sodium chloride 0.98 oz., and borax 
0.35 oz., are dissolved, with the aid of heat, in 6 to 8 quarts of 
water, and the solution is boiled for 10 hours, the water lost 
by evaporation being constantly replaced. The results ob- 
tained with this bath were not much better than with Bottger's. 

Jordis obtained useful results from a platinum lactate bath 



446 ELECTRO-DEPOSITION OP METALS. 

prepared by transposition from platinic sulphate with ammon- 
ium lactate. There are, however, difficulties in obtaining 
platinic sulphate of uniform composition.* 

Management of 'platinum baths. Copper and brass may be 
directly plated with platinum, but iron, steel and other metals 
are first to be coppered, otherwise they would soon decompose 
the platinum bath, independent of the fact that an unexcep- 
tionable deposit cannot be produced ujjon them without the 
cementing intermediary layer of copper. 

Platinum baths must be used hot, and even then require an 
electro-motive force of 5 to 6 volts, and hence, in plating with 
a battery at least three, or better four, Bunsen cells must be 
coupled one after the other. An abundant evolution of gas 
must appear on the objects and anodes. The anode-surface- 
(platinum anodes) must not be too small, and should be only 
at a few centimeters' distance from the objects. Since the 
platinum anodes do not dissolve, the content of platinum in 
the bath decreases constantly, and the bath must from time to 
time be strengthened. For this purpose, the bath, prepared 
according to Bottger's formula, is heated in a porcelain dish 
or enameled vessel to the boiling-point, a small quantity of 
fresh solution of sodium citrate is added and platoso-ammon- 
ium chloride introduced so long as solution takes place. A 
concentrated solution of platoso-ammonium chloride in sodium 
citrate (so-called platinum essence) may be kept on hand and 
a small quantity of it be at intervals added to the bath. Baths 
prepared according to the English method are strengthened 
by the addition of platinum chloride. 

Execution of platinum plating. The objects, thoroughly freed 
from grease and, if necessary, coppered, are suspended in the 
bath heated to between 176° and 194° F., and this tempera- 
ture must be maintained during the entire operation. The 
current should be of sufficient strength and the anodes placed 
so close to the objects that a liberal evolution of gas appears 

* Jordis, Die Elektrolyse wasseriger Metallsalzlosungen, 1901. 



DEPOSITION OF PLATINUM AND PALLADIUM. 447" 

on them. For plating large objects, it is recommended to go- 
round them, at a distance of 0.31 to 0.39 inch, with a hand- 
anode of platinum sheet which should not be too small and 
should be connected to the anode-rod. When the current has 
vigorously acted for 8 to 10 minutes, the objects are taken 
from the bath, dried and polished. However, for the produc- 
tion of heavy deposits — for instance, upon points of lightning 
rods — the deposit is vigorously brushed with a steel-wire 
scratch-brush or fine pumice-powder. The objects are then 
once more freed from grease and returned for 10 or 15 minutes 
longer to the bath to receive a further deposit of platinum 
with a weaker current, which must, however, be strong enough 
to cause the escape of an abundance of gas-bubbles. The 
objects are then taken out, and after immersion in hot water, 
dried in sawdust. The deposit is then well burnished, first 
with the steel tool and finally with the stone, whereby the 
gray tone disappears and the deposit shows the color and 
luster of massive platinum sheet. Points of lightning-rods 
platinized in this manner were without flaw after an ex- 
posure to atmospheric influences for more than six" years. 

For plating directly, without previous coppering, iron,, 
nickel, cobalt and their alloys with platinum, the following 
process has been patented in Germany : * Nickel or cobalt is 
first electrolytically deposited upon base metals fusing with 
difficulty, such as, iron, nickel, cobalt, or their alloys, for 
instance, nickel steel, a suitable bath for this purpose being 
composed of nickel-ammonium sulphate 290 parts, ammonium 
sulphate 75, citric acid 20, distilled water 4000. The metal 
is then heated in a reducing hydrogen atmosphere at 1652° 
to 1832° F., this operation being repeated after each elec- 
trolytical treatment in the platinum bath. The latter is best 
composed of: Platinum-ammonium phosphate 25 parts, 
sodium phosphate 500, distilled water 4000. 

The advantage claimed for this process is that the deposit, 

♦German patent 201664. 



448 ELECTRO-DEPOSITION OF METALS. 

of platinum does not peel off even when exposed to great heat, 
as is the case with an alloy previously coppered, and that by 
frequently repeating the operation the content of platinum 
steadily increases until the deposit finally possesses the prop- 
erties of pure platinum. 

Recovery of platinum from platinum solutions. From not too 
large baths, precipitation of the platinum with sulphuretted 
hydrogen is the most suitable method, and preferable to evap- 
orating and reducing the metal from the residue. The pro- 
cess is as follows : Acidulate the platinum solution with hydro- 
chloric acid ; and, after warming it, conduct sulphuretted 
hydrogen into it. The metal (together with any copper pres- 
ent) precipitates as sulphide of platinum. The precipitate is 
filtered off, dried, and ignited in the air, whereby metallic 
platinum remains behind. From larger baths the platinum 
may be precipitated by suspending bright sheets of iron in the 
acidulated bath. In both cases the precipitated platinum is 
treated with dilute nitric acid in order to dissolve any copper 
present. After filtering off and washing the pure platinum, 
dissolve it in aqua regia. The solution is then evaporated to 
dryness in the water bath, and the chloride of platinum thus 
obtained may be used in making a fresh bath. Precipitation 
■by zinc sheets or zinc dust can also be recommended. 

2. Deposition of Palladium. 

Properties of palladium. Palladium, when compact, has a 
white color and possesses a luster almost equal to that of sil- 
ver. Its specific gravity is about 12.0 ; it is malleable and 
ductile, and may be fused at a white heat. In the oxy- 
hydrogen flame it is volatilized, forming a green vapor. It is 
less permanent in the air than platinum. It is dissolved by 
nitric acid ; it is scarcely attacked, however, by hydrochloric 
or sulphuric acid. Hydriodic acid and free iodine coat it 
with the black palladium iodide. 

On account of the high price of its salts, palladium has been 
but little used for electro-plating purposes; nor, for the same 



DEPOSITION OF PLATINUM AND PALLADIUM. 449 

reason, is it likely to be more extensively employed in the 
future. 

According to M. Bertrand, the most suitable bath consists of 
•a neutral solution of the double chloride of palladium and 
-ammonium, which is readily decomposed by 3 Bunsen cells 
•coupled one behind the other (therefore about 5.4 volts). A 
sheet of palladium is used as anode. 

A solution of palladium cyanide in potassium cyanide does 
•not yield as good results as the above bath. 

Palladium is entirely constant in the air, and in color 
■closely resembles silver. It possesses further the property of 
not being blackened by sulphuretted hydrogen, and for this 
reason it is sometimes employed for coating silver-plated 
metallic articles. 

Palladium has also of recent years been employed for 
plating watch movements. According to M. Pilet, 4 milli- 
grammes (about T V grain) of palladium are sufficient to coat 
the works of an ordinary-sized watch. M. Pilet recommends 
the following bath : Water 2 quarts, chloride of palladium 5| 
drachms, phosphate of ammonia 3| ozs., phosphate of soda 
17J ozs., benzoic acid 2f drachms. 

Deposits of iridium and rhodium have recently been pro- 
duced from baths similar in composition to those mentioned 
under palladium. But as these metals would be used for 
plating purposes only in isolated cases, it is not necessary to 
<enter into details. 
29 



CHAPTER XL 

DEPOSITION OF TIN, ZINC, LEAD AND IRON, 
i. Deposition of Tin (Sn = 119 parts by weight). 

Properties of tin. Tin is a white, highly lustrous metal. It 
possesses but little tenacity, but has a high degree of mallea- 
bility, and tin-foil may be obtained in leaves less than ^V-h 
of a millimeter in thickness. Tin melts at about 446° F., 
and evaporates at a high temperature. The fused metal shows 
great tendency to crystallize on congealing. By treating the 
surface of melted tin with a dilute acid, the ciystalline struc- 
ture appears in designs (moire metallique), resembling the ice- 
flowers on frosted windows. 

Tin remains quite constant even in moist air, and resists 
the influence of an atmosphere containing sulphuretted hy- 
drogen. Strong hydrochloric acid quickly dissolves tin on 
heating, hydrogen being evolved and stannous chloride 
formed. Dilute sulphuric acid has but little action on the 
metal ; when heated with concentrated sulphuric acid, sulphur 
dioxide is evolved. Dilute nitric acid dissolves tin in the 
cold without evolution of gas ; concentrated nitric acid acts 
vigorously upon the metal, whereby oxide of tin, which is 
insoluble in the acid, is formed. Alkaline lyes dissolve the 
metal to sodium stannate, hydrogen being thereby evolved. 

Tin baths. The bath used by Roseleur for tinning with the 
battery works very well. It is composed as follows : 

I. Pyrophosphate of soda 3.5 ozs., tin salt (fused) 0.35 oz., 
water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, 1.25 volts. 

Current density, 0.25 ampere. 

To prepare the bath dissolve the pyrophosphate of soda in 

(450) 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 451 

10 quarts of rain water, suspend the tin-salt in a small linen 
bag in the solution, and move the bag to and fro until its 
contents are entirely dissolved. 

Objects of zinc, copper and brass are directly tinned in this 
bath. Articles of iron and steel are first coppered or prelimi- 
narily tinned by boiling in a bath. given later on under tinning 
by contact, the deposit of tin being then augmented in bath I 
with the battery current. Cast-tin anodes as large as possible 
are used, which, however, will not keep the content of tin in 
the bath constant. It is therefore necessary, from time to 
time, to add tin-salt, which is best done by preparing a solu- 
tion of 3.5 ozs. of pyrophosphate of soda in 1 quart of water 
and introducing into the solution tin-salt as long as the latter 
dissolves clear. Of this tin-essence add to the bath more or 
less, as may be required, and also augment the content of 
pyrophosphate of soda, if notwithstanding the addition of tin- 
salt, the deposition of tin proceeds sluggishly. 

Though the bath composed according to formula I suffices 
for most purposes, an alkaline tin bath, first proposed by 
Eisner, and later on recommended by Maistrasse, Fearn, Birg- 
ham and others, with or without addition of potassium cyan- 
ide, may be mentioned as follows : 

II. Crystallized tin-salt 0.7 ozs., water 1 quart, and potash 
lye of 10° Beaume until the precipitate formed dissolves. 

As seen from the formula the solution of tin-salt is com- 
pounded with potash lye of the stated concentration (or with 
a solution of 1 oz. of pure caustic potash in water), until the 
precipitate of stannous hydrate again dissolves. 

Some operators recommend the addition of 0.35 oz. of potas- 
sium cyanide to the solution. 

In testing Salzdde's bronze bath (p. 363), it was found to 
yield quite a good deposit of tin directly upon cast iron, and it 
was successfully used for this purpose by omitting the cuprous 
chloride, and using instead 0.88 oz. of stannous chloride, so 
that the composition became as follows : 

Ila. 98 per cent, potassium cyanide 3.5 ozs., carbonate of 



452 ELECTRO-DEPOSITION OF METALS. , 

potassium 35£ ozs., stannous chloride 0.88 ozs., water 10 
quarts. With 4 volts a heavy deposit was rapidly obtained. 

Very good results were obtained in a hot bath (158° to 194° 
F.), first made public by Neubeck, which consists of: 

III. 70 per cent, caustic soda 35| ozs., ammonium soda 
35| ozs., fused tin-salt 7 ozs., water 10 quarts. 

Electro-motive force at 10 cm. electrode-distance, and 155° 
F., 0.8 volt. 

Current-density 1 ampere. 

The chemicals are sufficiently dissolved in the water. 
When the bath commences to work sluggishly, about 0.35 to 
0.5 oz. of fused tin-salt has to be added. 

Management of tin baths. — Tin baths should not be used at 
a temperature below 68° F. Too strong a current causes a 
spongy reduction of the tin, which does not adhere well, while 
with a suitable current-strength quite a dense and reguline 
deposit is obtained. Cast-tin plates, with as large a surface as 
possible, are used as anodes. ' The choice of the tin-salt exerts 
some influence upon the color of the tinning. By using, for 
instance, crystallized tin-salt, which is always acid, in prepar- 
ing the bath according to formula I, a beautiful white tinning 
with a bluish tinge is obtained, which, however, does not 
adhere so well as that produced with fused tin-salt. Again, 
the latter yields a somewhat dull gray layer of tin, and there- 
fore the effects of the bath will have to be corrected by the 
addition of one or the other salt. 

As previously mentioned, iron and steel objects are best sub- 
jected to a light preliminary tinning by boiling. However, 
instead of this preliminary tinning, they may first be electro- 
coppered and, after scratch-brushing the copper deposit, 
brought into the tin bath. 

Process of tin-plating. — From what has been said, it will be 
evident that the execution of tin-plating is simple enough. 
After being freed from grease, and pickled, the objects are 
brought into the bath and plated with a weak current. For 
Iheavy deposits the objects are frequently taken from the bath 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 453 

and thoroughly brushed with a brass scratch-brush, not too 
hard, and moistened with dilute sulphuric acid (1 part acid 
of Q6° Be. to 25 water) and, after rinsing in water, are re- 
turned to the bath. If, with the use of too strong a current, 
the color of the deposit is observed to turn a dark dull gray, 
scratch-brushing must be repeated. When the tinning is 
finished the articles are brushed with a brass scratch-brush 
and decoction of soap-root, then dried in sawdust, and polished 
with fine whiting. 

For tinning by contact and boiling, see special chapter, " Depo- 
sitions by Contact." 

2. Deposition op Zinc (Zn = 65.37 parts by weight). 

Properties of Zinc. Zinc is a bluish-white metal, possessing- 
high metallic luster. It melts at 776° F. At the ordinary 
temperature zinc is brittle, but it is malleable at between 212° 
and 300° F., and can be rolled into sheets. At 392° F. it 
again becomes brittle, and may be readily reduced to powder. 
The specific gravity of zinc varies from about 6.86 to 7.2. 
When strongly heated in the air, or in oxygen, it burns with 
a greenish-white flame, producing dense white fumes of the 
oxide. 

In moist air it becomes coated with a thin layer of basic 
carbonate, which protects the metal beneath from further 
oxidation. Pure zinc dissolves slowly in the ordinary mineral 
acids, but the commercial .article containing foreign metals is 
rapidly attacked, hydrogen being evolved. 

Since zinc is a very electro-positive metal and precipitates 
most of the heavy metals from their solutions, especially cop- 
per, silver, lead, antimony, arsenic, tin, cadmium, etc., this 
being the reason why in dissolving impure zinc, the admixed 
metals do not pass into solution so long as zinc in excess is 
present. Potash and soda lyes attack zinc, especially when it 
is in contact with a more electro-negative metal, hydrogen 
being evolved. 

Zinc in contact with iron protects the latter from rust, and 
also prevents copper from dissolving when in contact with it. 



454 ELECTRO-DEPOSITION OF METALS. 

Up to within a few years, objects were, as a rule, zincked 
by the so-called galvanizing process, and electro-plating with 
zinc was only used for parts which could not stand hot gal- 
vanizing, for instance, finer qualities of cast-iron objects or 
parts of machines, such as parts of centrifugals for sugar 
houses. 

Further researches and practical experience in this line led 
to the application of zinc by the electrolytic cold process to 
other objects, such as sheet-iron and iron for constructive pur- 
poses. Thus, for instance, all the iron in lengths of up to 36 
feet and 7 feet 6 inches projection used in the construction of 
the palm houses in the new botanical garden at Dahm en- 
Berlin were electro-plated with a thick deposit of zinc, and 
thorough investigations by the authorities have shown that, 
as regards protection from rust, the iron thus plated with zinc 
is at least not inferior to iron zincked by the hot process. 

Electro-zincking has also proved of value for protecting the 
tubes of the Thornycroft boiler and several plants of this char- 
acter are now in operation. Of great importance is also the 
electro-zincking of iron and steel network for corsets. 

Electro-zincking is also of great advantage for small iron 
articles, for instance, screws and nuts, since the worms do not 
fill up with metal, as is the case in the hot process, and con- 
sequently do not require re-cutting. 

While in the further manipulations, such as bending, 
punching, etc., of sheets, angle-iron, T-iron, pipes, etc., 
zincked by the hot galvanizing process, the layer of zinc 
readily cracks off, the electro-deposit adheres very firmly, if 
the basis-metal has been properly cleansed ; and if the de- 
posit is not of excessive thickness, which would be entirely 
useless, it cannot be detached by bending and beating. If it 
be further taken into consideration that in zincking by the 
hot galvanizing process much more zinc than is necessary for 
the protection against rust adheres to the objects, that the loss 
of zinc by the formation of hard zinc (an iron-zinc alloy) is 
considerable, and that it is quite expensive to keep the plant 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 455 

in repair, it will 'have to be admitted that in an economical 
aspect also, zincking with the assistance of the current pre- 
sents many advantages. 

Exhaustive comparative experiments regarding zincking by 
the hot process and by electro-deposition (cold process), have 
been published by Burgess.* These experiments relate to the 
duration of protection of the basis-metal, adhering power of 
the zinc coating, ductility and flexibility of the latter, uni- 
formity of the coatings as regards strength and density, as 
well as resistance against mechanical wear. The results of 
the experiments were as follows : 

The disadvantages of hot galvanizing are : Considerable 
•consumption of heat and a material loss of zinc by oxidation 
on the surface of the fused zinc, by alloying with the cover of 
sal-ammoniac, and by the formation of hard zinc — a zinc-iron 
alloy which is formed at the expense of the walls of the iron 
•tank. Burgess estimates the loss of zinc at 50 per cent, of the 
sine used, and only a portion of it can be regained by a special 
process. 

On the other hand, in electro-zincking no loss by heat is 
incurred, and hence such articles as steel-wire, steel-springs, 
etc., can be zincked, the treatment of which, at the tempera- 
ture of the melted zinc, would be out of the question. Elec- 
tro-zincking of certain kinds of work is now specified by the 
Governments of Great Britain and Germany, and the United 
States Government has installed at its various shipyards com- 
plete equipments for the purpose of treating articles by the 
electrical method. 

The loss of zinc in electro-zincking is nominal and the wear 
of the vessels used is less than 10 per cent, per annum, while 
in the hot process it amounts to from 50 to 100 per cent. 

By electro-deposition articles of any size may be zincked ; 
the bath is always ready for use, and the thickness of the coat- 
ing can be controlled and regulated, which in hot galvanizing 

* Lead and Zinc News, 1904, viii, Nos. 8 to 10. 



456 ELECTRO-DEPOSITION OF METALS. 

is possible only to a limited degree. Both processes possess 
the drawback of never yielding coatings of uniform thickness ; 
the edges of hot-zincked pieces, especially of those which 
come last from the bath, are smeared over, i. e., they are more 
heavily zincked than others, while, by reason of the current- 
density being greater on these portions, the edges of sheets- 
zincked by electro-deposition are also more heavily zincked 
than parts in the center of the sheets. 

The usual method of determining, by immersion in a 20 per 
cent, copper sulphate solution, the thickness of the coating of 
zinc obtained by hot-galvanizing, was found by Burgess to 
be quite unsuitable for judging the thickness and quality of 
electro-zincking. This test, known as Preece's test, consists 
in placing the galvanized iron in the copper solution for J to 
1 minute, and continuing the immersions until the test-piece- 
shows a red deposit of copper, which is a true indication that 
the zinc has been penetrated and the iron exposed. In Ger- 
many it is as a rule required that hot-galvanizing must stand! 
for at least 30 seconds constant immersion before the red cop^ 
per color appears ; so long as the coating of zinc is intact there- 
is only a black coloration. On applying Preece's test to elec- 
tro-zincked articles it was found that they would not stand as^ 
many immersions in the copper solution as coatings obtained 
by hot-galvanizing, but nevertheless they were more resisting 
to atmospheric influences. For testing the power of resistance- 
of the coatings, Burgess therefore made use of dilute sulphuric 
acid, and found that an electro-deposited coating J the weight 
of one produced by hot-galvanizing possesses the same power 
of resisting corrosion as the latter, and that for coatings of" 
equal thickness the proportion of the resisting power is as 
10 : 1. This superiority of electro-zincking has to be ascribed 
to the greater purity of the deposit effected by electron 
deposition. 

On measuring the adhesive power, Burgess ascertained quite- 
different values from those of hot-galvanizing. With electro- 
deposited zinc the force required to tear the coatings from the- 



DEPOSITION OP TIN, ZINC, LEAD AND IRON. 457 

basis-metal (iron) amounted on an average to 482 lbs. per 
square inch, and only to 280 lbs. for coatings obtained by 
hot-galvanizing. Hence the adhesive power of electro- 
deposited coatings is materially greater. 

Attempts were made to ascertain the ductility and flexibility 
of the coatings by rolling. However, no positive results were 
obtained, some deposits becoming thereby more or less cracked, 
while others remained intact. The flexibility of the deposit is 
without doubt affected by the reaction of the bath, and it has 
been observed that from very slightly acid electrolytes, with 
an electro-motive force of 1.5 amperes, deposits free from cracks 
were obtained while very brittle deposits were obtained from 
more strongly acid solution with the same current-density. 
Burgess's experiments in this respect only made sure of the 
fact that there is no material difference in the behavior of 
hot- and cold-galvanized sheets with coatings of equal thick- 
ness. In all cases the zinc, when subjected to rolling, showed 
a tendency to separate from the basis-metal ; the zinc detached 
from electro-zincked sheet, however, possessed greater strength' 
and was less brittle than that from hot-galvanized sheet. 

On examining the detached coatings under the microscope 
it was further found that, contrary to the generally accepted 
opinion, the coating produced by hot-galvanizing was far more 
porous than that obtained by electro-deposition. An electro- 
deposit of less than 100 grammes zinc per square meter sur- 
face, was to be sure also porous, but with a thickness of 200 • 
grammes zinc per square meter the pores had grown together. 

The resistance against mechanical wear was apparently 
the same with the different deposits of equal thickness. Only 
in one case the electro-deposit proved of less value, than the- 
hot-galvanizing, namely, when electro-zincked sheets were 
subjected by heating and cooling to frequent and considerable 
changes in temperature, blisters were more frequently formed, 
and the zinc became detached to a greater extent than was- 
the case with hot-galvanized sheet. This shows that electro- 
zincked sheets should not be used for heating pipes for high- 



458 ELECTRO-DEPOSITION OF METALS. 

temperatures. Blistering is less to be feared with tempera- 
tures not exceeding that of steam of 3 atmospheres. 

Zinc baths. While flat articles can be readily coated with 
a firmly-adhering layer of zinc of uniform thickness, the pro- 
duction of such a deposit upon large, shaped articles and pro- 
filed objects is attended with difficulties, because zinc baths do 
not work quite well in the deeper portions. As will be seen 
later on, these difficulties may be overcome, on the one hand, 
by heating the baths and, on the other, by the use of anodes 
with somewhat the same profile as the article to be zincked, 
so that all portions of it are as nearly as possible at the same 
distance from the anodes. 

In plating articles with depressions, better results are ob- 
tained by depositing not pure zinc, but zinc in combination 
with other metals. Of course, zinc must be largely in excess 
if the deposit is to have the same effect as pure zinc in pro- 
tecting the plated article from rust. By the addition of salts 
of magnesium and aluminium to the zinc bath, Schaag, Dr. 
Alexander and others have endeavored to deposit zinc in com- 
bination with these metals. While the possibility of deposit- 
ing aluminium from aqueous solutions is doubtful, it is very 
likely that in Schaag's, as well as in Dr. Alexander's patented 
process neither the magnesium nor the aluminium is the 
effective agent, but the tin or mercury salts which are also 
added to the bath. But such additions are nothing new, since 
deposits of zinc-tin alloys with or without mercury salts have 
for many years been produced. The same object is attained 
by an addition of tin and nickel to the zinc bath, and experi- 
ments have conclusively shown that deposits upon iron pro- 
duced in such a bath protect the iron from rust as well as a 
deposit produced in a bath of pure zinc, or in Dr. Alexander's 
zinc baths, the patents for which are now expired. The good 
effect of aluminium sulphate .in zinc baths might solely be 
due to the fact that the acidity of the baths is longer main- 
tained. 

In connection with the Alexander patent it may here be 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 459 

stated that an important decision was rendered by Judge 
Cross of the Circuit Court of the United States for the District 
of New Jersey, in favor of the Hanson & Van Winkle Co., of 
Newark, N. J., and Chicago, 111., and against the United States 
Electro-Galvanizing Co. of Brooklyn, owners of these patents. 
The decision ends as follows : " For the following, among 
other reasons, then, the defendant does not infringe ; it does 
not make the alloyed coating of the patent, employs no basic 
salts, but rather makes and maintains throughout an acid 
bath ; does not use chloride of aluminium in its salts, does not 
use any organic substance with its salts or bath, or any equiva- 
lent thereof, and its bath is composed in part of different in- 
gredients from the complainants, is prepared differently and 
under different conditions, and its ingredients, in so far as they 
are the same, appear in the different proportions. The bill of 
complaint will accordingly be dismissed, with costs." 

Whatever may be said of the validity of the Alexander 
patents as against others, as against the salts and processes of 
the Hanson & Van Winkle Co., the patent is of no effect. 
The largest cold galvanizers of this country have been fitted 
up by the experts of this company. 

While the protection against rust of deposits from alloy- 
baths is about the same as from pure zinc baths, the use of the 
latter, without the addition of foreign metals can nevertheless 
be recommended, since with a suitable composition of the bath 
and proper arrangement of the anodes perfect zinc deposits 
can in all cases be obtained. 

During the last few years several investigations regarding 
the electrolysis of zinc have been made and numerous propo- 
sitions have been advanced, but space will not permit to con- 
sider them here. According to 0. Hildebrand very satis- 
factory results are obtained with the so-called regenerative 
process, a lead plate being used as anode instead of a zinc 
anode. Solution of zinc sulphate in water, to which is added 
a small quantity of sulphuric acid, is employed as electrolyte. 
By the use of a regenerative vat charged with zinc dust, the 



460 ELECTRO-DEPOSITION OF METALS. 

electrolyte is kept constantly in circulation and regenerated 
by coming in contact with the zinc dust in the regenerative vat. 

By this method zinc coatings of good quality are obtained. 
The deposit is almost free from impurities, adheres firmly to 
the iron and is more uniform than that obtained by the hot 
galvanizing process. The zinc being used in the form of 
finely divided zinc dust the electrolyte comes in intimate con- 
tact with it and consequently is very quickly neutralized. 
Besides the drawbacks connected with the use of zinc anodes 
are avoided. As disadvantages may be mentioned the con- 
siderably greater electro-motive force required with the use of 
insoluble lead anodes and the consequently larger cost of 
current, and further, the operating expenses caused by the- 
apparatus forcing the bath-liquor into the regenerating vats. 

Dr. Szirmay and von Kollerich want to add solution of 
magnalium (aluminium-magnesium alloy) in sulphuric acid 
and dextrose to white vitriol (zinc sulphate) solution. In 
dissolving magnalium, aluminium sulphate and magnesium 
sulphate are formed. Neither aluminium or magnesium in 
watery solutions are reducible as metals by the current, as 
they oxidize at the moment of reduction, water being decom- 
posed. The effect of the aluminium sulphate with its acid 
reaction is simply that the bath does not readily become alka- 
line, while the magnesium sulphate acts as a conducting salt r 
the separated magnesium-ions of it causing the secondary re- 
duction of zinc from the sulphate solution. The addition of 
carbohydrates to which dextrose belongs, which became 
known through the English patent No. 12691, 1897, is 
claimed to prevent the formation of sponge, which, however, 
according to experiments made in Dr. Langbein's laboratory, 
is the case only to a limited extent. An addition of dextrose 
appears to have the further effect of the bath working better 
in the deeper portions and the deposits turning out less 
tufaceous. The deposits frequently come from the bath with 
a slight luster, this being especially the case when electrotysis 
is for some time continued after the addition of the dextrose. 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 461 

According to Goldberg (German patent 151336) an addi- 
tion of pyridine to zinc baths is claimed to effect a dense de- 
posit of zinc of a beautiful white color and velvety appearance. 
On testing this process these claims were found to'be correct, 
and furthermore such a bath works better in the depression. 

Classen has patented the addition of "glucosides, and claims 
to obtain thereby the deposition of lustrous zinc coatings. 

The reason why in baths of the compositions formerly 
:given, actually thick deposits without showing a spongy 
structure could not be obtained, is found in the fact that these 
baths contained too little metal and had an unsuitable, gen- 
erally alkaline, reaction. Even when electrolysis has only 
been carried on for a short time, alkaline baths do not yield 
a coherent and purely metallic deposit of zinc, a basic zinc 
oxide being reduced together with the metallic zinc, which 
readily gives rise to the formation of sponge. 

The formula for an alkaline zinc bath, namely, 3 \ ozs. of 
white vitriol dissolved in 1 quart of water, and adding potash 
■lye until the precipitated zinc hydroxide is again dissolved, 
which was given in former editions of this work, yields quite 
fair results. This bath works best when, in place of potash 
or soda lye, ammonia is used for precipitating and dissolving 
the zinc hydroxide, and the bath contains a large excess of 
-ammonia. Hence, in the above-mentioned formula, the 
potash lye should be replaced by ammonia and, in addition 
to the quantity required for the solution of the precipitate 
formed, enough of it should be used to impart to the bath a 
strong odor of ammonia. However, by reason of this odor of 
ammonia, the operation of such a bath becomes disagreeable, 
and even injurious to health. 

In order to force the bath to work better in the deeper 
portions, mercury salts in the form of potassium-mercuric cya- 
nide may be added to alkaline baths. It must, moreover, be 
borne in mind that an addition of mercury is of advantage 
because the anodes are thereby superficially amalgamated and 
•kept in a purely metallic state. In alkaline zinc baths par- 



462 ELECTRO-DEPOSITION OF METALS. 

ticularly, an abundant coat of zinc hydroxide is formed upon 
the anodes, and because this coat does not dissolve to the same 
extent as it is formed, it has to be frequently removed by 
mechanical means. 

Below formulas for zinc baths which have stood the test for 
a long time are given. 

I. Chemically pure crystallized zinc sulphate 44 lbs., pure 
crystallized sodium sulphate 8.8 lbs., chemically pure zinc 
chloride 2.2 lbs., crystallized boric acid 1.1 lbs., dissolved in 
water to a 100-quart bath. 

Electro-motive force at 10 cm. electrode-distance and at 64.4° 
F., 1.1, 1.5, 1.8, 2.2, 2.4, 2.7, 3.7 volts. 

Current-density at 64.4° F., 0.55, 0.75, 0.95, 1.15, 1.25, 1.45 r 
1.9 amperes. 

Electro-motive force at 10 cm. electrode-distance and at 113 a 
F., 0.9, 1.05, 1.25, 1.40, 1.8, 2.0, 2.3, 3.5 volts. 

Current-density at 113° F., 0.7, 0.8, 1.0, 1.1, 1.4, 1.55, 1.8, 
2.75 amperes. 

This bath, as well as others of similar composition, will 
stand considerably higher current-densities if provision is 
made for vigorous agitation of the electrolyte. If agitation is 
to be avoided, an increase of the content of zinc salt and boric 
acid is of advantage. 

To prepare the bath, dissolve the zinc sulphate, the zinc 
chloride and sodium sulphate (Glauber's salt) in luke-warm 
water. Heat a portion of this fluid to about 194° F., dissolve 
in- it the boric acid, and mix it with the other solution. An 
addition of 0.8 to 1 oz. of dextrose per quart is recommended. 

For the production of a good deposit of zinc it is of im- 
portance to use zinc salts free from other metals, it having 
been shown that a content of foreign metals, especially iron, 
causes disturbances. 

The reaction of the bath should be kept slightly acid, so 
that blue litmus paper is intensely reddened, but congo paper 
is not perceptibly blued. The bath gradually loses its acid 
reaction and does not work as well, the deposit becoming 



DEPOSITION OP TIN, ZINC, LEAD AND IRON. 463- 

darker instead of pale gray, and inclining towards the forma- 
tion of sponge. It should then be acidulated by the addition 
of pure dilute sulphuric acid. For flat objects (sheets, etc.) 
the bath may be used cold, but for profiled objects, such as 
angle-iron, beams, etc., it is advisable to heat it between 104° 
and 122° F. 

II. Crystallized sodium citrate 5.5 lbs., chemically pure 
zinc chloride 8.8 lbs., pure crystallized ammonium chloride 
6.6 lbs. Dissolve with water to a 100-quart bath. 

Electro-motive force at 10 cm. electrode-distance and at 64.4° 
F., 0.8, 1.0, 1.5, 1.8, 2.2, 3.4 volts. 

Current-density at 64.4° F., 0.7, 0.9, 1.4, 1.7, 1.9, 3.0 am- 
peres. 

Electro-motive force at 10 cm. electrode-distance and 113° F.,. 
0.8, 1.0, 1.5, 1.75, 2.5, 3.2 volts. 

Current-density at 113° F., 1.0, 1.25, 1.9, 2.3, 3.2, 4.3 am- 
peres. 

The bath is prepared by dissolving the constituents in the 
water, which should not be too cold ; best luke-warm. What 
has been said under formula I in reference to the reaction 
also applies to this bath. 

III. Wm. Schneider* recommends a bath of the following 
composition : Water 1 gallon, sulphate of zinc 2 lbs., sulphate 
of aluminium 2 ozs., glycerine | oz. Electro-motive force: 10 
amperes to 1 square foot of surface. The work must be agi- 
tated while being coated. The use of pure zinc anodes is 
imperative if satisfactory results are to be obtained, and the 
iron to be plated must be perfectly clean. If this solution 
is carefully attended to it will plate a good light gray, and by 
the addition of a few of the various reagents of which there 
are several, such as glue and dextrine, on the market, a very 
bright deposit of zinc can be obtained. 

Zinc anodes. Treatment of zinc baths. For anodes it is best 
to use very pure rolled-zinc sheets 0.11 to 0.19 inch or more 

* Metal Industry, No. 9, 1909. 



464 ELECTRO-DEPOSITION OF METALS. 

in thickness. Strips of zinc riveted to the anodes with zinc 
rivets serve for suspending the anodes to the anode rods. For 
-zincking sheet-iron, wires, etc., on a large scale, cast zinc 
anodes may be preferred on account of being cheaper. It 
must, however, be borne in mind that cast anodes readily 
- crumble, especially when they have frequently to be cleansed 
mechanically by scraping and scratch-brushing for the removal 
of the basic zinc salts forming on them. The loss of zinc 
• caused by the formation of basic zinc salt and by crumbling 
is considerable, and according to Cowper-Coles may be as 
large as 30 per cent, of the entire consumption of zinc. This 
estimate, however, appears to be excessive; to be sure the 
formation of a coat on the anodes as well as the crumbling of 
the anodes is disagreeable, but it cannot be considered a direct 
loss since the zinc salt as well as the detached crumbs of 
metal can, by dissolving in sulphuric acid, be converted into 
zinc sulphate, and the latter be used for strengthening the 
bath. The surface of the anodes should be as large as possible. 
Rolled anodes also become readily coated with a layer of basic 
zinc salt, and it is advisable from time to time to remove this 
layer by scratch-brushing. The coating thus removed may 
be dissolved in dilute sulphuric acid and added to the bath 
as neutral zinc solution. As previously mentioned, the zinc 
baths should show a perceptibly acid reaction in order to 
avoid as much as possible the formation of sponge, and there- 
fore the reaction should at short intervals be tested and, if 
necessary, corrected by the addition of dilute sulphuric acid. 

The zinc anodes should be removed from the bath when 
the latter is not in operation, otherwise the free acid of ,the 
bath would be neutralized by the solution of zinc and it would 
i have to be again acidified. 

Although the zinc baths, without exception, work Well at a 
temperature of 64.4° to 68° F. upon flat articles, it is recom- 
mended, in view of the slight electro-motive force required, to 
keep them somewhat warmer. 

For zincking strongly-profiled objects it is advisable to heat 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 465 

the baths to between 104° and 113° F., since at a higher 
temperature the deposit penetrates better into the deeper por- 
tions. Anodes with profiles similar to those of the objects are 
used. As shown by the current conditions given with the 
formulas for the baths, a fixed current-density is not obligatory 
in electro-zincking. For the bath, according to formula I, 
1.25 to 1.5 amperes may be designated as the lowest rational 
■current-density, at which 5.29 to 6.34 ozs. of zinc per square 
meter (10.76 square feet) are in one hour deposited. With 
heated and agitated baths, the maximum current-density may 
be given as about 3 amperes, with which 12.91 ozs. of zinc per 
square meter are in one hour deposited. However, in certain 
•cases, this current-density may be exceeded. For baths, ac- 
cording to formula II, it is best to use a slighter current- 
density. Should it, however, be necessary to work with 
higher current-densities, provision has to be made for a suffi- 
ciently acid reaction and thorough agitation in order to avoid 
the formation of sponge. In zincking, agitation of the baths 
is of special value, and, if possible, should never be omitted. 

Tanks for zinc baths. — For smaller baths it is best to use 
stoneware vessels, while for larger baths, tanks of pitch-pine, 
■or still better, of wood lined with lead, may be employed. 
•Zinc salt solutions gradually impair the swelling capacity of 
wood, and even pitch-pine tanks, most carefully built, com- 
mence in the course of time to leak. For this reason tanks of 
wood lined with lead, or of sheet-iron, deserve the preference. 
Brick tanks lined with cement may also be used, provided 
several coats of thinly-fluid asphalt lacquer be applied to the 
cement lining to prevent the latter from being attacked by the 
-acid baths. 

Heating the zinc baths is best effected by steam introduced 
through a hard lead (alloy of antimony and lead) coil on the 
bottom of the tank. 

Execution of zincking. — Since the principal object of electro- 
zincking is to prevent rusting, embellishing the metallic ob- 
jects being only in very rare cases effected, the mechanical 
30 



466 ELECTRO-DEPOSITION OF METALS. 

refinement of the surface by grinding is as a rule omitted, a 
purely metallic surface free from scale being produced in a 
cheaper manner. 

This is done by pickling, scratch-brushing, scrubbing with 
sand in a drum, or by the sand-blast. The latter deserves the 
preference for large quantities of , small articles, as well as for 
objects with not too large surfaces. For freeing large surfaces 
of sheet from scale, the use of the sand-blast is, however, too 
expensive on account of the great consumption of power, and, 
besides, takes too much time. 

In electro-zincking particularly, the mode of operating de- 
pends entirely on the nature and form of the objects, and it is, 
therefore, advisable to discuss separately the various manipu- 
lations required for certain objects. 

Zincking sheet-iron. When the sheets have been freed from 
grease by means of hot alkaline tyes or lime paste, they are 
pickled in dilute sulphuric or hydrochloric acid, and the 
loosened scale is removed by scouring with fire brick and 
sand. The use of a pickle of hydrochloric acid 2 parts, sul- 
phuric acid of 66° Be., 1 part, and water 17 parts is also of 
advantage. To what extent the electrolytic method of pick- 
ling, previously referred to, can be used to advantage for this 
purpose, has thus far not been practically determined. By 
the use of a sand-blast the cleanest and most complete results 
are obtained, but the expense for power has to be taken into 
consideration. 

As in all other electrc-plating processes, a purely metallic 
surface free from scale is an absolutely necessary condition for 
a well-adhering deposit of zinc. Portions of the sheets coated 
with scales, would come out zincked, but in the further 
manipulation of the sheets, the layer of zinc becomes de- 
tached, and this must be avoided. 

The pickled and scoured sheets, generally in lengths of 6 
feet and 1 foot wide, are secured to binding screws and brought 
into the zinc bath, that given under formula I being especially 
suitable for the purpose. Heating the bath to between 104° 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 467 

and 113° F., and vigorous agitation by blowing in air, or by- 
means of a mechanical contrivance, allows of working with a 
current-density of 2J amperes, and, if necessary, more, at 
which a sufficiently heavy deposit to protect the objects from 
rust is in 20 to 25 minutes obtained. 

In working on a large scale, it is advisable to couple the 
baths in series and to zinc in each bath 3 sheets, each 2x1 
meters, with a total surface of 12 square meters per bath. 
Hence, for zincking the sheets on both sides and working with 
a current-density of 2.5 amperes per square decimeter, there 
will be required four baths in series, each with 12 square 
meters of surface, a dynamo of 12 x 250 = 3000 amperes, and 
the electro-motive force should be 12 volts, 2 J to 3 volts be- 
ing required per bath. With such a plant working for 10 
hours, 340 to 360 sheets, each 2x1 meters, can be zincked on 
both sides so as to protect them from rust, and by working 
day and night, 820 to 850 sheets. 

When zincking is finished, the sheets are rinsed in water, 
then immersed in boiling water until they have acquired the 
temperature of the latter, and finally set up free, or hung up 
to dry. The hot sheets then dry in a few minutes. 

The zincked sheets show a pale-gray, mat, velvety appear- 
ance, and are generally used in this state. If the zinc deposit 
is to be lustrous, the sheets are scratch-brushed, best dry, with 
steel scratch-brushes. 

Zincking of pipes. The pipes are freed from scale either by 
means of the sand blast or by pickling and scouring. To 
protect the screw threads from the pickle, they are coated 
with tallow which, however, previous to zincking, has to be 
removed with hot soda lye or rubbing with benzine, and care 
must be had thoroughly to free them from grease with lime 
paste. 

The pipes, best four or six pieces one above the other, are 
placed upon a frame which also serves for conducting the cur- 
rent, and, if they are of considerable diameter, it is advisable 
to turn them 90° when half the time for zincking has expired, 
in order to obtain a uniform deposit. 



4G8 ELECTRO-DEPOSITION OF METALS. 

While in zincking straight flat sheets, the distance of the 
anodes from the cathodes need only be 1.96 to 2.35 inches, 
the distance of the zinc anodes from the pipes should be the 
greater, the larger the diameter of the latter is. Pipes of very- 
large diameter are best suspended alongside each other, instead 
of one above the other, a row of anodes of zinc sheet suitably 
bent being arranged between every two pipes. Frequent 
turning of the pipes is required, and uniform zincking is pro- 
moted by heating the bath and by vigorous agitation. The 
further manipulation of the zincked pipes is similar to that 
given for sheets. 

Zincking the insides of the pipes is a more difficult opera- 
tion. To commence with, it is as a rule a difficult task to 
find out whether pickling and scratch-brushing has been 
sufficiently done and a pure metallic surface have everywhere 
been produced. Special directions for inside zincking depend 
partly on the diameter, and it can only be said in general that 
it is best to zinc the pipes while in a vertical or half-lying posi- 
tion and to provide for a constant renewal of the electrolyte in 
the interior. 

Zincking of wrought-iron girders, "Y-iron, [J -iron, \_-iron, etc. 
The cheapest plan of freeing the objects from scale is by pick- 
ling in dilute sulphuric or hydrochloric acid and vigorous 
scrubbing with sand, or scratch-brushing. The use of a trans- 
portable sand blast is also very suitable, but this method is 
more expensive than the former. 

For the uniform zincking of such profiled objects, the use of 
flat zinc anodes is not practicable, far more zinc being deposited 
upon the edges and surfaces next to the anodes than upon the 
depressed portions. Hence, in addition to heating and vig- 
orously agitating the bath, recourse must be had to profiled 
anodes corresponding to the shape of the object to be zincked, 
the object of such profiled anodes being solety to bring all por- 
tions of the objects at as nearly an equal distance as possible 
from the anodes. 

The profiled anodes may be made by bending zinc sheets 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 



469 



into the proper shape, or what is better, by riveting or screw- 
ing square cast-zinc bars to the zinc sheets, this being of ad- 
vantage, for instance, in zincking girders. Figs. 132 and 133 
show the arrangement of the anodes, and require no further 
explanation. 

In zincking profiled objects it is of advantage to add to the 
bath prepared according to formula I, 0.8 oz. of dextrose per 
quart, the bath working better in the deeper portions with 



Fig. 132. 



Fig. 133. 





such an addition than without it. Of still greater advantage 
is the pyridine-zinc bath according to Goldberg. 

Zincking of wire, steel tapes, cords, etc. — Under this heading 
will chiefly be considered iron and steel wire which is to be 
protected from rust by a deposit of zinc. As previously men- 
tioned when speaking of nickeling wire, the latter has to be 
uncoiled and passed at a suitable rate of speed through the 
pickling solutions and the zinc bath. 

Bright-drawn iron and steel wire, requiring but little prepar- 
atory work, is most suitable for zincking. It suffices for coils 
of such wire, when free from rust, to push them upon a shaft 
of corresponding diameter, and bring the whole into a tank 
with hot soda lye, which is furnished with bearings for the 



4 70 ELECTRO-DEPOSITION OF METALS. 

•shaft. From this tank the wire, freed from grease by the hot 
lye, passes through a few felt rolls or cloth cheeks supplied 
with thin lime paste, an additional freeing from grease being 
thus, for the sake of greater security, effected. The wire is 
then brought under a rose for the removal by water of adher- 
ing lye and lime, then slides over a metallic roll which is in 
contact with the negative pole of the source of current, and 
passes into the zinc bath. In the latter zinc anodes are 
arranged below and above the lengths of wires running parallel 
to each other. Such zinc baths for wire zincking are from 20 
to 26 feet long. The average velocity with which wire 0.039 
inch in diameter passes through the bath is about 20 feet per 
minute. For wire of less diameter the velocity may be in- 
creased to 59 feet, while for wire of greater diameter it has to 
be correspondingly decreased. 

When the wire comes from the bath it is conducted through 
a tank containing boiling water, and is then reeled up. The 
contrivances for reeling up the wire are best driven by an 
electro-motor with the use of a starting resistance for regu- 
lating the turns, it being thus possible to choose and change 
at will the velocity of the passage of the wire in the bath. 

Zincking of wires produced by rolling is not quite so 
simple. Such wire, which is readily recognized by its black 
appearance, is coated with a scale, which adheres very firmly 
by reason of the rolling process. Previous to zincking, such 
wire has to be carefully freed from scale in order to obtain 
a purely metallic surface. This may be accomplished in 
various ways, the method selected depending on the nature 
and properties of the material to be manipulated. 

Experiments in cleansing such wire by means of the sand 
blast did not yield satisfactory results, the process being too 
slow notwithstanding the use of suitable annular blast-pipes. 
Hence recourse will have to be had to pickling in acids, but 
many kinds of wire and steel tapes stand pickling only for a 
very short time, as they readily become brittle. AVire which 
does not show this drawback is pickled until the scale is par- 



DEPOSITION OF TIN, ZINC. LEAD AND IRON. 471 

tially dissolved, or at least very much loosened. After rinsing 
in water, it is immersed in boiling water so that it will dry 
rapidly and then, for the removal of the loosened scale, passed 
by means of a suitable contrivance through the scratch-brush- 
ing machine. Wire which will not bear pickling at all, or 
only for a very short time, has to be brightened by mechanical 
means, either by the drawing-plate, or by conducting it over 
revolving, hard grindstones or emery wheels provided with 
insertions for holding it. 

Zincking of screws, nuts, rivets, nails, tacks, etc. Such small 
objects are freed from grease either by means of the sand blast 
or in tumbling barrels with the use of wet, sharp sand. When 
the latter process is employed, the objects have of course to be 
immediately zincked to prevent rusting. 

For zincking quantities of such small objects, one of the 
mechanical plating contrivances referred to under " Deposi- 
tions of Nickel " is very suitable. When zincking is effected 
in baskets the position of the objects has to be frequently 
•changed by stirring in order to insure a uniform deposit. 

The bath prepared according to formula II, when heated, 
is very well adapted for zincking small objects in large quan- 
tities. With the use of a mechanical plating apparatus, it is 
possible in consequence of the constant agitation, to work with 
high current-densities and to deposit a correspondingly large 
quantity of zinc in a comparatively short time. 
' The further manipulation of the zincked small objects con- 
sists in washing them in baskets and drying them quickly by 
immersion in boiling water and shaking with heated clean 
sawdust, though the latter operation may be omitted. 

For zincking by 'contact, see special chapter " Depositions by 
•Contact." 

Zinc alloys. — The production of the principal zinc alloy, 
brass, by the electric method, having already been mentioned, 
•and also that of a -zinc-nickel-copper alloy (German silver), it 
remains to give an alloy of zinc with tin, or of zinc, tin and 
nickel, which can be produced by the same means. 



472 ELECTRO-DEPOSITION OP METALS. 

A suitable bath for depositing this alloy consists of: Chlo- 
ride of zinc 6f drachms, crystallized stannous chloride 9 
drachms, pulverized tartar 9 drachms, pyrophosphate of soda 
2| drachms, water 1 quart. Dissolve the salt at a boiling 
heat, and filter the cold solution, when it is ready for use. For 
anodes, cast plates of equal parts of tin and zinc are used. 

These deposits have no special advantages, but, on the other 
hand, a deposit containing zinc in large excess has the same- 
effect of protecting iron from rust as a deposit of pure zinc. 

By preparing a bath which contains as conducting salt 
sodium citrate, and ammonium chloride and the chlorides of 
the metals in the proportion of 4 zinc chloride to 1 tin chloride, 
a deposit is obtained, which not only is a perfect protection 
against rust, but also enters far better into depressions than 
pure zinc. By adding to the bath a small quantity of chlo- 
ride of mercury, or of nickel, alloys of zinc, tin, mercury, or 
of zinc, tin and nickel are formed, which are distinguished 
from pure zinc deposits by a finer structure. 

2. Deposition or Lead (Pb = 207.10 parts by weight). 

The properties of lead onty interest us in so far as it is less 
attacked by most mineral acids than any other metal, and 
against the action of such agents. For decorative purposes 
electro-deposits of lead are scarcely used, and those as a pro- 
tection against chemical influences cannot be produced of 
sufficient thickness for that purpose. 

Lead baths. — I. Dissolve, by continued boiling, caustic pot- 
ash 1.75 ozs. and finely pulverized litharge 0.17 oz. in 1 quart 
of water. 

II. According to Watt, the following solution is used : 
Acetate of lead 0.17 oz., acetic acid 0.17 oz., water 1 quart. 

The bath prepared according to formula I deserves the- 
preference. 

Lead baths require anodes of sheet-lead or cast-lead plates, 
a weak current and, in order to produce a dense deposit of 
some ' thickness, the objects have to be frequently scratch- 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 473- 

brushed. Iron is best previously coppered. Peroxide of lead 
is separated on the anodes, and they have to be frequently 
cleansed with a scratch-brush. The formation of peroxide of 
lead on the anodes is utilized for the production of the so- 
called Nobili's rings (electrochromy). 

Metallo- chromes (Nobili's rings, iridescent colors, electro- 
chromy). The reduction of peroxide of lead upon the anodes 
or upon objects suspended as anodes, produces superb effects 
of colors. For the production of such colors, a bath is pre- 
pared by boiling for half an hour 3| ozs. of caustic potash,. 
14 drachms of litharge, and 1 quart of water. The operation 
is as follows : Suspend the articles, carefully freed from grease 
and pickled, to the anode-rods, and with a weak current intro- 
duce in the lead solution a thin platinum wire connected with, 
the object-rod by flexible copper wire, without, however, touch- 
ing the article. The latter will successively become colored 
with various shades — yellow, green, red, violet and blue. By 
the continued action of the current, these colors pass into a 
discolored brown, which also appears in the beginning if the 
current be too strong, or if the platinum wire be immersed too- 
deep. Such unsuccessful coloration has to be removed by 
rapidly dipping in nitric acid, and, after rinsing in water,, 
suspending the article in the bath. For coloring not too large 
surfaces, a medium-sized Bunsen cell is. as a rule, sufficient, if 
the platinum wire be immersed about § inch. 

Colors of all possible beautiful contrasts may be obtained^ 
by perpendicularly placing between the objects to be colored' 
and the platinum wire a piece of stout parchment paper, or 
providing the latter with many holes or radial segments. 

Another process of producing these effects of colors is as 
follows : Prepare a concentrated solution of acetate of lead 
(sugar of lead), and after filtering, pour it into a shallow porce- 
lain dish. Then immerse a plate of polished steel in the 
solution, and allow it to rest upon the bottom of the dish. 
Now connect a small sheet of disc copper with the wire pro- 
ceeding from the zinc element of a constant battery of two on- 



474 ELECTRO-DEPOSITION OF METALS. 

three cells, the wire connected with the copper element being 
placed in contact with the steel plate. If now the copper disc 
be brought as close to the steel plate as possible without touch- 
ing it, in a few moments a series of beautiful prismatic colora- 
tions will appear upon the steel surface, when the plate should 
be removed and rinsed in clean water. These colorations are 
films of lead in the form of peroxide, and the varied hues are 
due to the difference in thickness of the precipitated peroxide 
-of lead, the light being reflected through them from the pol- 
ished metallic surface beneath. By reflected light every pris- 
matic color is visible, and by transmitted light a series of 
prismatic colors complementary to the first colors will appear 
-occupying the place of the former series. The colors are seen 
to the greatest perfection by placing the plate before a window 
with the back to the light, and holding a piece of white paper 
•at such an angle as to be reflected upon its surface. The 
colorations are not of a fugitive character, but will bear a 
■considerable amount of friction without being removed. In 
proof of the lead oxide being deposited in films or layers, it 
-may be stated that if the deposit be allowed to proceed a few 
seconds beyond the time when its greatest beauties are exhib- 
ited, the coloration will be less marked, and become more or 
-less red, green or brown. If well rubbed, when dry, with the 
-finger or -fleshy part of the hand, a rich blue-colored film will 
be laid bare 'by the removal of the delicate film above it. 

The plan recommended by Mr. Gassiot to obtain the metallo- 
• chromes is to place over the steel plate a piece of cardboard or 
parchment paper cut into some regular design, and over this a 
rim of wood, the copper disc being placed above this. Very 
beautiful effects are obtained when a piece of fine copper wire 
is turned up in the form of a ring, star, cross or other pattern, 
and connected with the positive electrode, this being in fact 
one of the simplest and readiest methods of obtaining the 
colorations upon the polished metal. Metallochromy is ex- 
tensively employed in Nuremberg to ornament metallic toys. 
It has been adopted in France for coloring bells, and in 



DEPOSITION OP TIN, ZINC, LEAD AND IRON. 475 

Switzerland for coloring the hands and dials of watches. In 
using the lead solutions to produce metallochromes, it must 
be remembered that metallic lead becomes deposited upon the 
cathode, consequently the solutions in time become ex- 
hausted, and must therefore be renewed by the addition of 
the lead salt. 

For the preparation of iridescent sheets, i. e., nickeled zinc 
sheet coated with peroxide of lead, a sheet of lead of the same 
size as the sheet to be made iridescent is used as object, and 
a current of about 2J volts is employed. The slime formed 
in the bath must from time to time be removed, as otherwise 
the tones of color will not turn out pure. 

4. Deposition of Iron (Fe = 55.85 parts by weight) (Steeling). 

The principal practical use of the electro-deposition of iron 
as to coat printing plates of softer metal to increase their wear- 
ing qualities. We are indebted to Bottger for calling attention 
to the employment of iron deposits, but notwithstanding the 
■efforts of many scientific and practical men to improve the 
process, the expectation entirely to replace copper galvano- 
plasty for cliches by iron-galvanoplasty has not been fulfilled. 

Only such baths as are suitable for steeling will here be 
given. Solutions for the production of thick iron deposits, 
and the conditions under which they can be obtained, will be 
referred to later on under " Galvanoplasty in Steel." 

Iron (steel) baths. I. According to Varrentrapp: Pure green 
vitriol 4| ozs., ammonium chloride 3J ozs., water 1 quart. 

Electro-motive force at 10 cm. electrode-distance, 1.0 volt. 

Current-density, 0.2 ampere. 

Boil the water for \ hour to expel all air, and, after cooling, 
add the green vitriol and ammonium chloride. By the action 
of the air, and the oxygen appearing on the anodes, this bath 
is readily decomposed, insoluble basic sulphate of iron being 
separated as a delicate powder, which has to be frequently 
removed from the fluid by filtering. To decrease decomposi- 
tion, the double sulphate of iron and ammonium, which can 



476 ELECTRO-DEPOSITION OF METALS. 

be more readily obtained pure and free from oxide, may be 
used. 

II. Ammonium chloride 3J ozs., water 1 quart. 
Electro-motive force at 10 cm. electrode distance. 1.0 volt. 
Current-density, 0.2 ampere. 

This neutral solution of ammonium chloride may be made 
into an iron bath by hanging in it iron sheets as anodes, sus- 
pending an iron or copper plate as cathode, and allowing the 
current to circulate until a regular separation of iron is at- 
tained, which is generally the case in 5 to 6 hours. Although 
a separation of hydrated oxide of iron also takes place in this 
bath, it does so in a less degree than in that prepared accord- 
ing to formula I. For the production of not too heavy a 
deposit of iron, some operators claim to have obtained the 
best results with this bath. 

According to Bottger, the following bath serves for steeling : 

Ila. Potassium ferrocyanide (yellow prussiate of potash) 0.35 
oz., Rochelle salt 0.7 oz., distilled water 200 cubic centimeters. 
To this solution is added a solution of 1.69 drachms of persul- 
phate of iron in 50 cubic centimeters of water, whereby a 
moderate separation of Berlin blue takes place. Then add, 
drop by drop, whilst stirring constantly, solution of caustic 
soda until the blue precipitate has disappeared. The clear,, 
slightly yellowish solution thus obtained can be used directly 
for steeling. 

A heavy and very hard deposit of iron is obtained in a 
bath of the following composition. 

III. Ammonio-ferrous sulphate 1^ ozs., crystallized citric 
acid 0.88 oz., water 1 quart ; sufficient ammonia for neutral 
or slightly acid reaction. 

E leer o-motive force at 10 cm. electrode-distance, 2.0 volts. 

Current-density, 0.3 ampere. 

Management of iron baths. As previously mentioned, the 
insoluble precipitate from time to time formed in the bath 
has to be removed by filtration. This precipitate is, however, 
very delicate, and when stirred up might settle upon the 



DEPOSITION OF TIN, ZINC, LEAD AND IRON. 477 

objects and prevent the adherence of the deposit. It is, there- 
fore, advisable to use for steel baths, tanks of much greater 
depth than corresponds to the height of the objects, whereby 
the stirring-up of the sediment in suspending the objects is 
best avoided. 

With the use of steel anodes the baths may become readily 
acid. This can be avoided by suspending a few small linen 
bags filled with carbonate of magnesia in the bath. On the 
other hand, anodes of soft iron make the electrolyte alkaline, 
and when such anodes are employed, the reaction of the bath 
must from time to time be tested and the neutral reaction be 
restored by the addition of very dilute sulphuric acid, or better, 
citric acid. 

Deposits produced in an iron bath which has become alka- 
line show slight hardness, form very rapidly with a mat ap- 
pearance and have a tendency to peel off. 

Execution of steeling. — The cleansed and pickled objects are 
placed in the baths according to formulae I and II, with a 
current of 1.5 to 2 volts, and the anodes at a distance of 4 to 
4f inches, after which the current is reduced to 1 volt. To 
produce iron deposits of any kind of thickness, the escape of 
the hydrogen bubbles which settle on the objects must be pro- 
moted by frequent blows with the finger upon the object-rod. 
When steeling is finished, the articles are thoroughly rinsed, 
then plunged into very hot water, and, after drying in sawdust, 
placed for several hours in a drying chamber heated to about 
212° F., to expel all moisture from the pores. 

Steeling of printing plates has the advantage over nickeling, 
that when the plates are worn they can be rapidly freed from 
the deposit by dilute sulphuric acid or very dilute nitric acid, 
and resteeled. It has been ascertained by experiments that 
the capability of resistance of steeled plates is less than that of 
nickeled plates, 200,000 impressions having been made with 
the latter without any perceptible wear. 

For steeling printing plates a bath prepared according to 
formula II or III is very suitable. 



CHAPTER XII. 

DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM.. 
1. Deposition of Antimony (Sb — 120.2 Parts by Weight).. 

Properties of antimony. — Electro-deposited antimony pos- 
sesses a gray luster, while native, fused antimony shows a 
silver-white color. Antimony is hard, very brittle, and may 
easily be reduced to powder in a mortar. It melts at 842° F., 
and at a strong red heat takes fire and burns with a white 
flame, forming the trioxide. Its specific gravity is 6.8. It is 
permanent in the air at ordinary temperatures. Cold, dilute, 
or concentrated sulphuric acid has no effect upon antimony, 
but the hot concentrated acid forms sulphide of antimony. 
By nitric acid the metal is more or less energetically oxidized^ 
according to the strength and temperature of the acid. 

Antimony baths. — Electro-depositions of antimony are but 
seldom made use of in the industries, though they are very 
suitable for decorative contrasts. This is no doubt due to the 
fact that a thoroughly reliable bath yielding deposits without 
the appearance of drawbacks during the operation is thus far 
not known. 

For the special study of electro-depositions of antimony we 
are indebted to Bottger and Gore, the latter having discovered 
the explosive power of deposits of antimony deposited from a 
solution containing chloride or hydrochloric acid. 

According to Gore, a bath consisting of tartar emetic 3 ozs., 
tartaric acid 3 ozs., hydrochloric acid 4|- ozs., and water, 1 
quart, yields a gray, crystalline deposit of antimony. This 
bath requires a current of about 3 volts. The deposit possesses 
the property of exploding when scratched or struck with a 
hard object. The explosion is attended by a cloud of white 

(478) 



DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 479'< 

vapor, and sometimes by a flash of light, considerable heat 
being always evolved. This explosibility is due to a content 
of antimony chloride. Bottger found 3 to 5 per cent, of chlo- 
ride of antimony in the deposit, and Gore 6 per cent. A 
similar explosive deposit is obtained by electrolyzing a simple 
solution of chloride of antimony in hydrochloric acid (liquid 
butter of antimony, liquor stibii chlorati) with the current. 

A lustrous, non-explosive deposit of antimony is obtained 
by boiling 4.4 ozs. of carbonate of potash, 2.11 ozs. of pulver- 
ized antimony sulphide, and 1 quart of water for 1 hour, re- 
placing the water lost by evaporation, and filtering. Use the 
bath boiling hot, employing cast antimony plates or platinum 
sheets as anodes. 

An antimony bath which yields good results is composed as 
follows : 

Schlippe's salt If ozs., water 1 quart. Dissolve the salt in 
the water. Electro-motive force required, 4 volts. An un- 
pleasant feature of this bath is that during electrolyzing sul- 
phuretted hydrogen escapes, which limits its application. 

2. Deposition of Arsenic (As 74.96 parts by weight). 

Properties ■ of arsenic. — Arsenic has a gray- white color, a 
strong metallic luster, is very brittle, and evaporates at a red 
heat. In dry air arsenic retains its luster, but soon turns dark 
in moist air. It is scarcely attacked by dilute hydrochloric 
and sulphuric acids, while concentrated sulphuric acid, as well 
as nitric acid, oxidizes it to arsenious acid. If caustic alkalies 
are fused together with arsenic, a portion of the latter is con- 
verted into alkaline arsenate. 

Arsenic baths. — Arsenic solutions are extensively used in the 
plating room for decorative purposes in order to produce blue- 
gray to black tones of a certain warmth, which are very effec- 
tive in combination with bright copper, brass, etc. 

For coloring all kinds of metals blue-gray the following 
solutions are very suitable : 

I. Pulverized white arsenic If ozs., crystallized pyrophos- 



480 ELECTRO-DEPOSITION OF METALS. 

phate of soda 0.7 oz., 98 per cent, potassium cyanide If ozs., 
water 1 quart. 

Dissolve the. pyrophosphate of soda, and the potassium 
•cyanide in the cold water, and after adding, whilst stirring, 
the arsenic acid, heat until the latter is dissolved. In heat- 
ing, fumes containing prussic acid escape, the inhalation of 
which must be carefully avoided. The bath is used warm, 
and requires a vigorous current of at least 4 volts, so that, at 
•the least, 3 Bunsen cells have to be coupled for electro-motive 
force. After suspending the objects they are first colored 
black-blue, the color passing with the increasing thickness of 
the deposit into pale blue, and finally into the true arsenic 
gray. Platinum sheets or carbon plates are to be used as 
anodes. 

In place of the bath prepared according to formula I, a 
solution of the following composition may be used : 

II. Sodium arsenate If ozs., 98 per cent, potassium cyanide 
0.8 oz., water 1 quart. Boil the solution for half an hour, then 
filter and use it at a temperature of at least 167° to 176° F., 
with a strong current. It yields a good deposit. 

Large baths, to be used cold, must be more concentrated, 
and require a stronger current than hot baths. 

When the baths begin to work irregularly and sluggishly, 
they have to be replaced by fresh solutions. 

The same rules as for other electro-plating processes are to 
be observed in depositing arsenic and antimony. 

However, attention may here be called to one feature 
which is frequently the cause of defective deposits. When, 
for instance, mountings of zinc, such as are used for book 
covers, jewel boxes, etc., are to be provided with a deposit of 
copper and arsenic, and hence are to show two colors, it is 
necessary to first copper them. After polishing and cleaning 
the coppered mountings, the places which are not to receive 
the blue-gray deposit of arsenic are coated with stopping-off 
varnish. When articles thus treated, after being again freed 
from grease and pickled, are brought into the arsenic bath, 



DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 481 

they frequently show ugly stains the size of a pin-head. 
This feature, however, does not appear when the articles be- 
fore being brought into the bath are drawn through water 
-acidulated with a small quantity of nitric acid (about % oz. 
of nitric acid to 1 quart of water), and thoroughly rinsed in 
•clean water. 

Mr. Emmanuel Blassett, Jr.,* gives the following solutions 
for coloring articles black : 

III. White arsenic 1 lb., potassium cyanide 2 lbs., water 6 
gallons, ammonium carbonate 10 ozs. 

Dissolve the white arsenic and potassium cyanide in 5 gal- 
lons of water, and the ammonium carbonate separately in 1 
gallon of water, and mix the two solutions. This solution is 
worked cold. Steel or brass anodes may be used and a cur- 
rent with the tension of 1 volt is sufficient. Without the 
ammonium carbonate the deposit is not so black and is in- 
clined to be steel-gray in color. It is a difficult operation to 
color small light pieces in this bath, possibly due to the poor 
conductivity of arsenic solutions. On very light articles the 
bath gives an iridescent color, or blue-black at the most. 
For this reason if a good black color is desired, the following 
dip should be used for small articles : White arsenic 2 ozs., 
potassium cyanide 5 ozs., water 1 gallon. 

This dip is used hot and without the current. The solution 
is made up in an enamel or agate ware vessel, and brought to 
•a boiling point by means of a gas stove. Work to be colored 
is fastened to wires or immersed in the solution by means of 
a plating or dip basket. Some platers make up a new dip 
every day or two, but by careful management, such as re- 
placing the water lost by evaporation and making small addi- 
tions of arsenic and cyanide, the dip may be made to last a 
long time. 

Another arsenic bath is made up as follows : 

* Metal Industry, March, 1913. 

31 



482 ELECTRO-DEPOSITION OF METALS. 

IV. White arsenic 3 lbs., potassium c} r anide 4 ozs., com- 
mercial caustic soda 1J lbs., water 5 gallons. 

The ingredients are boiled together. Soft steel or brass 
anodes are used, and a current of about 1 volt is required. 
A favorite bath with some platers is composed of: 

V. White arsenic 2 lbs., copper carbonate 4 ozs., potassium 
cyanide 2 \ lbs., water 5 gallons. 

In addition to the solutions described, which are all alka- 
line, there are several acid arsenic baths which are frequently 
employed. The most simple is composed as follows : 

VI. Muriatic acid 5 gallons, white arsenic 2 lbs. 

Carbon anodes are often used in operating this solution, and 
for that reason it is often spoken of as the " carbon solution." 
Acid solutions are indispensable on work where a portion of 
the surface is stopped off with an asphalt paint or varnish. 
Strong alkaline solutions ordinarily will remove paint or var- 
nish and spoil the finish, unless unusual care is exercised. 

A well-known acid bath is composed as follows : 

VII. Muriatic acid 1 gallon, iron filings 4 ozs., white 
arsenic 4 ozs. 

This formula is very suitable for producing an oxidized 
brass effect. The coating is a little heavier, as ircm is de- 
posited simultaneously with the arsenic. The deposit is soft, 
and may be easily relieved for a cut through finish. In all 
acid baths it is best to use either carbon or brass anodes. If 
iron or steel anodes are used, they are attacked by the acid, 
producing a very concentrated solution. Under such condi- 
tions particles of undissolved iron may interfere with the 
operation. 

Some platers prefer to use iron sulphate instead of iron 
filings and make up their solution as follows : 

VII. Muriatic acid 5 gallons, white arsenic 1 lb., iron sul- 
phate 1 lb. 

Electro-depositions of chromium, tungsten, cadmium and 
bismuth have thus far not become of any practical import- 
ance, and their discussion maj T , therefore, with good reason y 



DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 483 

be omitted. As regards silver-cadmium deposits the reader is 
referred to Areas-silvering under "Deposition of Silver." 

3. Deposition of Aluminium (Al = 27.1 Parts by Weight). 

There is actually no reason or authority for the heading of 
this section, but it has been introduced because inquiries are 
frequently received as to whether baths for the deposition of 
aluminium can be furnished. 

A number of receipts for the preparation of aluminium 
baths have been published, but in testing them nothing fur- 
ther could be obtained than the confirmation of the fact that 
the deposition of aluminium from aqueous solutions of its 
salts by the current upon the cathode has thus far not been 
feasible. 

Reports have from time to time appeared in newspapers of 
the iron construction of tall buildings having been provided 
with a heavy deposit of aluminium, and even the processes 
used have been fully described. It is to be regretted that 
such elaborate reports are even admitted into scientific jour- 
nals, though the separation of romance from truth could be 
readily accomplished by a conscientious examination. Un- 
scrupulous dealers offer their customers aluminium baths, 
charging a high price for them, and on testing a deposit pro- 
duced with such baths, it has frequently been found to consist 
solely of tin. Others, who actually had faith in the value of 
their invention have submitted for examination objects plated 
with aluminium by their processes. On testing such deposits 
it was found that in one case, it consisted of a thin deposit of 
zinc, the origin of which was due to zinckiferous aluminium 
salts, and in other cases, of a deposit of iron due to the same 
cause. 

The concurrence of the above-mentioned influences and the 
recent rapid development of the aluminium industry explains 
the demand for aluminium baths by many electro-platers. 
However, without entering into scientific reasons, which 
would not be within the scope of this work, it can here only 



484 ELECTRO-DEPOSITION OF METALS. 

be repeated that the reduction of metallic aluminium from its 
solutions will very likely remain an empty dream. 

4. Deposition upon Aluminium. 

The electro-deposition of other metals upon aluminium pre- 
sents many difficulties which are chiefly due to the behavior 
of this metal towards the plating baths. The deposits to be 
sure are formed, but they possess no adherence, and especially 
baths containing potassium cyanide yield the worst results in 
consequence of the effect of alkaline solutions upon the basis- 
metal. Since the production of aluminium has so largely 
increased, and a great number of articles of luxury and for 
practical use are now made of this metal, the need of decora- 
ting such articles by electro-plating or covering them entirely 
with other metals has been felt, since the color of aluminium 
is by no means a sympathetic one. Look into a show window 
where aluminium articles are exposed — nothing but gray in 
gray. Offended, the eye of the observer turns away, and 
seeks a more agreeable resting-place. 

Aluminium behaves so differently from other metals towards 
the cleansing agents generally used, that different methods 
from those previously described have to be employed in pre- 
paring it for plating. Nitric acid has almost no effect on 
aluminium, and pickle just a little ; but, on the other hand, 
the metal is attacked by concentrated hydrochloric acid, 
dilute hydrofluoric acid, and especially by alkaline lyes. 
Hence, if polished articles of aluminium are to be prepared 
for plating, alkaline lyes will have to be avoided in freeing 
them from grease, it being best to use only benzine for the 
purpose. Unpolished articles may without hesitation be freed 
from grease with caustic potash or soda lye, and, for the pro- 
duction of a dead white surface, be for a short time pickled in 
dilute hydrofluoric acid, and then thoroughly rinsed in run- 
ning water. 

For producing an electro-deposit upon aluminium it has 
foeen considered advisable to first copper the metal, and the 



DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 485 

Aluminium Gesellschaft of Neuhausen recommends for this 
purpose a solution of nitrate of copper. But the adherence of 
the copper proved also insufficient, because in the subsequent 
silvering, nickeling, etc., the deposit raised up. 

The copper bath recommended by Delval, consisting of 
sodium pryophosphate 3 ozs., copper sulphate (blue vitriol) 
| oz., sodium bisulphite f oz., water 1 quart, also proved 
unreliable. 

According to another patented process, plating of aluminium 
is claimed to be effected successfully, and without defect, by 
lightly coating the metal with silver amalgam by boiling in a 
silver bath compounded with potassium -mercury cyanide. 
However, this treatment did not always yield reliable results. 

According to Villon, articles of aluminium are to be im- 
mersed for one hour in a bath consisting of glycerin of ozs., 
zinc cyanide 0.88 oz., zinc iodide 0.88 oz., and then heated to 
a red heat. When cold, they are washed with a hard brush 
and water, and brought into the gold or silver bath. The suc- 
cess of this process seems also questionable. 

The best and most reliable process is without doubt the one 
patented, in 1893, by Prof. Nees. It consists in first immers- 
ing the aluminium articles previously freed from grease in caus- 
tic soda lye until the action of the lye upon the metal is recog- 
nized by gas bubbles rising to the surface. The articles with- 
out being previously rinsed are then for a few minutes immersed 
in a solution of 77 troy grains of chloride of mercury, rinsed, 
again brought into the caustic soda lye, and then, without 
rinsing, suspended in the silver bath. The deposit of silver 
thus obtained adheres very firmly, and can be scratch-brushed, 
and polished with the steel without raising up. It can also 
be directly gilded, brassed, or, after previous coppering in the 
potassium cyanide copper bath, provided with a heavy deposit 
of nickel and polished upon polishing wheels. 

Burgess and Hambuechen * found it best to first zinc the 

* Electro-chemical Industry, 1904, No. 3. 



486 ELECTRO-DEPOSITION OF METALS. 

aluminium in an acid zinc bath containing 1 per cent, fluoric 
acid ; the fluoric acid acts as a solvent upon the film of oxide 
formed so that the deposit is effected upon a pure metallic 
■surface. According to these authors, the aluminium article is 
to be immersed in dilute fluoric acid until its surface appears 
slightly rough and attacked. It is then to be rinsed in water, 
and for a few seconds immersed in a bath of sulphuric acid 
100 parts and nitric acid 75 parts. It is then again thoroughly 
rinsed in water, next brought into a zinc bath of 15° Be., con- 
sisting of zinc sulphate and aluminium sulphate, and acidu- 
lated with 1 per cent, of fluoric acid or the equivalent quan- 
tity of potassium fluoride, and zincked for 15 to 20 minutes. 
For subsequent silvering or gilding the zinc deposit is first 
coppered in the potassium cyanide copper bath. 

According to Gottig, a thin, firmly-adhering deposit of cop- 
per is first to be produced upon the aluminium by triturating 
blue vitriol solution with tin-powder and whiting ; or a tin 
deposit is to be produced by applying stannous chloride-ammo- 
nium chloride solution by means of a soft brass brush. 

The Mannesmann Pipe Works, Germany, produce durable 
electro-deposits by brushing the aluminium with solutions of 
sulphide of gold and sulphide of silver in balsam of sulphur * 
and volatile oils, and burning in the metals in a muffle, under 
exclusion of the air, at 840° to 930° F. Thin layers of metal 
which are reduced adhere firmly to the aluminium, and are 
then provided with an electro-deposit desired. According to 
a process patented by the same corporation, the articles are 
provided with a firmly adhering (?) film of zinc by immersing 
them in boiling solution of zinc dust in caustic soda, and are 
then electro-plated. 

However, in view of the fact that all the methods mentioned 
above partly yield uncertain results, it has recently been pro- 
posed first to provide the aluminium in readily-fusible metallic 
salts (cupric chloride, tin salt) with a coat of these metals, and 
then treat it further in aqueous electrolytes. 

* Solution of sulphur in linseed oil. 



CHAPTER XIII. 

DEPOSITION BY CONTACT, BY BOILING, AND BY FRICTION. 

If a sheet of metal, for instance, copper, be brought into a 
solution which contains the cations of a metal of slighter 
solution-tension (p. 61), for example, a solution of potassium- 
silver cyanide in water with an excess of potassium cyanide, 
which has been heated to about 158° F., the following process 
takes place : By the osmotic pressure (p. 49) the metal-ions, in 
this case silver-ions, are reduced upon the copper sheet, the 
osmotic pressure of the solution being thereby decreased. In 
■consequence of this decrease in the osmotic pressure, copper- 
ions can be forced into the solution by the solution-tension, 
while additional silver-ions are brought to separate upon the 
copper sheet. Hence, during the formation of the deposit, a 
solution of the metal to be coated in the case in question, cop- 
per, takes place at the same time, this process coming to a 
standstill when the copper sheet has been covered with a 
coherent coat of silver, which prevents further solution of 
■copper in the electrolyte. 

The process may also be explained in a different way, 
namely, that by the immersion in the silver solution the 
■copper is negatively charged, positive silver-ions being by 
reason of electrostatic attraction attracted and reduced on the 
•copper. 

The deposits produced in this manner are generally known 
as deposits by immersion, or when the electrolyte is highly 
heated, by boiling. 

The same process takes place when metallic objects are 
plated by applying by means of a brush or by friction an 

(487) 



488 ELECTRO-DEPOSITION OF METALS. 

electrolyte which contains a metal with slighter solution- 
tension than possessed by the metal of an object to be coated. 

Since the more electro-positive metals of the old series of 
electro-motive force possess a greater solution-tension than 
the electro-negative metals, it may be briefly stated, that 
electro-positive metals when immersed in suitable solutions of 
electro-negative metals reduce the latter, and, under certain 
conditions, become coated with them so that a coherent de- 
posit is formed. 

From the process above described, according to which re- 
duction only takes place till the electro-positive metal has been 
provided with a coherent coating of the electro-negative metal, 
it is plain. that such deposits can be only very thin and can- 
not be increased by continued action of the electrolyte, except 
recourse be had to other means. 

The process, however, is a different one when a deposit is to> 
be produced by the contact of one metal with another in an 
electrolyte. , If a copper sheet dipping in a potassium cyanide 
solution of potassium-silver cyanide be touched with an electro- 
positive metal, for instance, a zinc rod or a zinc sheet, the 
latter dipping also in the electrolyte, an electric current is- 
generated which reduces silver-ions on the copper-sheet, while 
on the zinc sheet zinc-ions are forced into solution. However, 
even when the copper sheet has been covered with a coherent 
deposit of silver, the reduction of the latter goes on in so far 
as the silver which is also reduced upon the zinc, and which 
interrupts contact with the electrolyte, as well as prevents- 
further migration of zinc-ions into the solution, is only from 
time to time removed. 

The contact processes can, however, be applied only to a 
limited extent. On the one hand, the formation of uniformly 
heavy deposits upon the metallic objects is excluded, because 
by reason of the greater current-densities appearing at the 
point of contact with the contact metal, a heavier reduction of 
metal takes place there than on the portions further removed 
from the point of contact, except the latter be freq uently- 



BY CONTACT, BY BOILING, AND BY FRICTION. 489' 

changed. On the other hand, the constant increase of dis- 
solved contact-metal in the electrolyte constitutes a drawback, 
and is the cause of the electrolytes, as a rule, giving out long, 
before their content of metal is exhausted. Finally, the 
reduction of metal upon the contact-metal is not a desirable 
feature. 

As contact-metals, zinc, cadmium and aluminium are chiefly 
used. In many cases, aluminium being a highly positive 
metal, considerably surpasses in its effect the first-mentioned, 
metals, and possesses the advantage of not bringing into the 
electrolyte, metals reducible by the current. Furthermore, 
the quantities of metal deposited upon the aluminium can be 
dissolved with nitric acid without materially attacking the 
contact-metal. Darlay has recommended magnesium as a 
contact-metal (German patent 127,464). It presents, however r 
no advantage, on the one hand, on account of its high price 
and, on the other, by reason of the deficient results in connec- 
tion with the baths of the above-mentioned patent. 

The electrolytes serving for depositions by contact must 
possess definite properties if they are to yield good results. 

Since the currents generated by contact are weak, the elec- 
trolyte should possess good conductivity, so that the reduction, 
of metal does not take place too slowly, and it must attack — 
chemically dissolve — the contact-metal, as a current can only 
be generated if such be the case. Let us consider, for instance, 
a well-known gold bath for hot gilding by contact, which con- 
tains in 1 quart of water 77 grains of crystallized sodium phos- 
phate, 46^ grains of caustic potash, 15^ grains of neutral chlo- 
ride of gold, and 0.56 oz. of 98 per cent, potassium cyanide- 
It will be found that only a slight portion of the potassium 
cyanide is consumed for the conversion of the chloride of gold, 
into potassium-gold cyanide, the greater portion of it serving 
to increase the conductivity of the electrolyte. The caustic 
potash, together with the sodium phosphate, effects the alka- 
linity of the bath which is required for attacking and dissolv- 
ing the contact-metal, whether it be zinc, cadmium, aluminium, 



490 ELECTRO-DEPOSITION OF METALS. 

or magnesium. The effect of the alkaline phosphate as such 
is claimed to be that the deposit of metal which results not 
•only upon the objects in contact with the contact-metal, but 
also upon the latter itself, does not firmly combine with it, 
but can be readily removed by scratch-brushing. 

For increasing the conductivity of electrolytes containing 
potassium cyanide, a greater or smaller excess of the latter is 
used either by itself or in combination with chlorides, for in- 
stance, ammonium chloride or sodium chloride, nearly all 
known baths for contact-deposition containing these salts in 
varying quantities. For nickel and cobalt baths, an addition 
•of ammonium chloride, in not too small quantity, is most 
suitable, it assisting materially the attack upon the contact- 
metal and may in some cases serve for this purpose by itself 
without the co-operation of an alkali. 

The attack on the contact-metal is most effectually pro- 
moted by sufficient alkalinity of the electrolyte, mostly in 
connection with chlorides, in a few rarer cases without chlo- 
rides, and as previously mentioned, occasionally by chlorides 
alone without the co-operation of an alkali. 

In judging the formulas for contact baths to be given later 
-on, the effects here explained will have to serve as a basis. 

Small objects in quantities are generally plated in baskets 
made of the contact-metal, and, as previously mentioned, the 
deposition of quantities of the same metal with which the 
objects are to be coated upon the contact-body cannot be 
avoided. To be sure, claim is made in a few patents to pre- 
vent deposition upon the contact-metal and to keep the con- 
tact-body free by certain additions, for instance, alkaline 
pyrophosphates and phosphates, but experiments failed to 
prove the correctness of these claims. 

The useless reduction of metal is one of the many weak 
points of the contact-process. The bath thereby becomes 
rapidly poor in metal, requires frequent refreshing or regen- 
eration, which as a rule is not so readily done, and thus in 
[practice the contact-process becomes quite expensive. It must 



BY CONTACT, BY BOILING, AND BY FRICTION. 491 

further be borne in mind that so soon as reduction of metal 
upon the contact-body takes place, the formation of a deposit 
upon the object ceases, this being the reason why only very 
thin deposits can be produced, which do not afford protection 
against atmospheric influences, and are not sufficiently re- 
sistant to mechanical attack. 

To avoid as much as possible the drawback of metal being 
reduced on the wrong place, Dr. G. Langbein & Co. use, ac- 
cording to a method for which a patent has been applied for, 
baskets of contact-metal, the outsides of the latter, which do 
not come in contact with the objects, being insulated from the 
electrolyte by enameling, or coating with hard rubber, cellu- 
loid or similar materials capable of resisting the hot solution. 
Or, they use baskets of contact-metal the outsides of which 
^re provided, either mechanically by rolling or welding, or 
electrolytically by deposition, with the same metal contained 
in solution in the electrolyte, the baskets being thus protected 
from the deposit ; while, in addition, a partial regeneration of 
the bath is in many cases attained. With certain combina- 
tions a portion of the electro-negative metal or alloy combined 
with the contact-metal or fixed insulated from it, passes into 
solution, and partly replaces the metal which has been with- 
drawn from the bath and deposited upon the objects. 

Further drawbacks of the contact process are, working with 
baths almost boiling hot, and the consequent evolution of 
«team which is injurious to the workmen as well as to the 
work-rooms. 

Hence, the contact process is suitable only for coating — so 
to say coloring — objects in large quantities with another 
metal, when no demands as regards solidity of the deposit are 
made. 

Nickeling by Contact and Boiling. 

According to Franz Stolba, articles can be sufficiently nick- 
eled in 15 minutes by boiling them, mixed with fragments of 
zinc in a solution of nickel sulphate. A copper kettle tinned 



492 ELECTRO-DEPOSITION OF METALS. 

inside is to be used. Since stains are readily formed by this 
process, especially when nickeling polished iron and steel 
articles, on the places where the metal to be nickeled comes in 
contact with the zinc, Stolba in later experiments omitted the 
zinc, and thus the contact process becomes a boiling process. 
The articles are to be boiled for 30 to 60 minutes in a 10 per 
cent, zinc chloride solution to which is added enough nickel 
sulphate to give the solution a deep green color. 

However, Stolba's process cannot be recommended to the 
nickel-plater. To be sure a thin nickel deposit of a light 
color might be obtained upon brass articles, but that on iron 
objects generally turned out dark and mostly stained. The 
nickeling is so thin that it will not stand polishing with any 
kind of pressure, and the cheapness claimed for the process is- 
quite illusive, the solution soon becoming useless by reason 
of the absorption of copper, iron, etc., from the metals to be- 
nickeled. 

For small articles, which are not to be nickeled with the- 
assistance of the current, one of the following processes is to- 
be preferred : 

By boiling a solution of 8| ozs. of nickel-ammonium sul- 
phate and 8^ ozs. of ammonium chloride in 1 quart of water,, 
together with clean iron filings free from grease, and introduc- 
ing into the fluid copper or brass articles, the latter become 
coated with a thin layer of nickel capable of bearing light} 
polishing. 

In place of iron filings, it is of greater advantage to bring 
the objects to be coated in contact with a piece of sheet-zinc 
of not too small a surface, or to nickel them in an aluminium 
basket. The hotter the solution is, the more rapidly coating 
with nickel is effected, and when the bath is made slightly 
alkaline with ammonia, iron objects also nickel quite well in. 
an aluminium basket. 

In place of the zinc contact, Basse & Selve use an aluminium 
contact for nickeling (as well as for coppering and silvering). 
According to the patent specification, objects nickel gray and 



BY CONTACT, BY BOILING, AND BY FRICTION. 493 

•show no metallic luster when brought in a zinc basket into a 
boiling solution of 20 parts of nickel-ammonium sulphate, 40 
parts ammonium chloride and 60 parts water, which, after 
the addition of a slight excess of ammonia and filtering, is 
rendered slightly acid with citric acid. By substituting for 
the zinc basket an aluminium basket, a lustrous, more firmly 
adhering layer of nickel is in about two minutes obtained. 

Still better results are obtained by keeping the bath slightly 
alkaline with ammonia or ammonium carbonate. 

A. Darlay has patented in France, as well as in Germany, a 
process of nickeling (as well as cobalting) by aluminium or 
magnesium contact. However, the object of the invention is 
not the aluminium contact, which has been known for a long 
time, nor the special kinds of baths, the compositions of which 
are similar to those of other known contact-baths, but the use 
of the aluminium or magnesium contact in connection with 
baths of exactly defined compositions. 

These patented baths fulfill nothing further than the general 
conditions given in detail on p. 487 et seq., and which are also 
fulfilled by most of the long known contact-baths as shown by 
the bath for gilding by contact (p. 489). Darlay's patent is, 
therefore, a combination-patent, and its right of existence ap- 
pears rather doubtful in view of the fact that Basse and Selve's 
patent has expired, and that baths of the composition of the 
Darlay electrolytes have long been known and used for 
deposition. 

Darlay's baths are brought into commerce by " Electro- 
metallurgie" under the name of autovolt baths, and in answer 
to many inquiries it may here be stated that for the reason 
given on p. 488, no heavier deposits can be produced with 
these autovolt baths, than with the contact process in general, 
and that this autovolt method shows the same drawbacks as 
all other contact processes. 

In his patent specification, Darlay gives the following com- 
position of the electrolyte which is to be used hot : 

Water 1 quart, nickel chloride 1\ drachms, sodium phos- 



494 ELECTRO-DEPOSITION OF METALS. 

phate 8£ ozs., ammonium chloride 11J drachms, ammonium 
carbonate and sodium carbonate each 4f drachms. 

The sodium phosphate is claimed to effect the production of 
a bright attacking surface of the contact-metal, and the sodium 
and ammonium carbonates, the alkaline reaction and, hence 
the generation of the current, by dissolving the aluminium, 
while the ammonium chloride produces good conductivity. 
As regards the action of alkaline pyrophosphates, the reader 
is referred to p. 489. 

The inventor asserts that the proportions given above have 
to be kept within quite narrow limits. With the exception of 
the nickel chloride, the quantities of sodium phosphate and of 
one of the other chemicals can without fear be increased 50 
per cent., the results thus obtained being still better than with 
Darlay's formula. 

The chemical process of Darlay's electrolyte consists no 
doubt in that a transposition takes place between the nickel 
chloride and the sodium phosphate, sodium chloride and 
nickel phosphate being formed, which are soluble in the excess 
of sodium phosphate, and are not precipitated by the alkaline 
carbonates. 

Hence the bath given on p. 259 under formula IX for 
nickeling with an external source of current, should be suit- 
able for contact-nickeling with aluminium, if the quantity of 
sodium phosphate be materially increased, the conductivity 
enhanced by the addition of ammonium chloride, and the so- 
lution of the aluminium promoted by adding caustic potash, 
caustic soda, or better, alkaline carbonates. 

Cobalting by Contact and Boiling. 

Cobalting by contact is readily accomplished with the use 
of the following bath : Crystallized cobalt sulphate 0.35 oz., 
crystallized ammonium chloride 0.07 oz., water 1 quart. Heat 
the bath to between 104° and 122° F., and immerse the pre- 
viously cleansed and pickled articles in it, bringing them in 
contact with a bright zinc surface not too' small ; for small 



BY CONTACT, BY BOILING, AND BY FRICTION. 495- 

articles a zinc basket may be used. In 3 or 4 minutes the 
coating is heavy enough to bear vigorous polishing. 

It is a remarkable fact that with aluminium-contact no 
satisfactory results are obtained in this bath, the reaction of 
aluminium in cobalt solutions thus appearing to be different 
from that in nickel solutions. What has been said in re- 
gard to Darla} r 's contact process for nickeling applies also to 
cobalting. 

For cobalting small objects in quantities, the reader is re- 
ferred to Warren's process, p. 324. 

Coppering by Contact and Dipping. 

According to Liidersdorff, a solution of tartrate of copper in 
neutral potassium tartrate serves for this purpose. A suitable 
modification of this bath is as follows : Heat 10 quarts of water 
to 140° F., add 2 lbs. of pulverized tartar (cream of tartar) 
free from lime, and 10| ozs. of carbonate of copper. Keep the 
fluid at the temperature above mentioned until the evolution 
of gas due to the decomposition of the carbonate of copper 
ceases, and then add in small portions, and with constant stir- 
ring, pure whiting until effervescence is no longer perceptible. 
Filter off the fluid from the tartrate of lime, separate and wash 
the precipitate, so that the filtrate, inclusive of the wash water, 
amounts to 10 or 12 quarts, and dissolve in it If ozs. of caustic 
soda and 1 oz. of 99 per cent, potassium cyanide. 

With zinc-contact the bath works somewhat slowly, but 
more rapidly with aluminium-contact. Zinc is coppered in 
this bath by simple immersion. 

The bath for coppering by contact, proposed by Weill, has 
been given on p. 334, under formula X. The bath is to be 
heated to between 185° and 194° F., and with zinc contact 
yields a tolerably good deposit upon small iron objects. With 
aluminium-contact, iron screws as well as iron articles in 
quantities are quickly and nicely coppered. 

According to Bacco, a copper bath in which zinc may be 
coppered by immersion, and iron and other metals in contact 



496 ELECTRO-DEPOSITION OF METALS. 

with zinc, is prepared by adding to a saturated solution of 
blue vitriol, potassium cyanide solution until the precipitate 
of cyanide of copper which is formed is again dissolved. Then 
add -iV to \ of the volume of liquid ammonia and dilute with 
•water to 7° Be. 

The bath is to be heated to 194° F. To the same extent 
as zinc passes into solution the copper bath is gradually 
changed to a brass bath. 

Every strongly alkaline copper cyanide bath may serve for 
coppering by contact, provided only a small quantity of free 
potassium cyanide is present in the bath, and the latter is 
heated to 194° F. 

Zinc when used as a contact-metal shows the drawback of 
"the copper depositing quite firmly upon it, so that it has to 
be removed by pickling in nitric acid. Furthermore, with 
the use of zinc as contact-bodies, the content of free alkali has 
to be much larger than with aluminium contacts, and so 
much zinc passes, in the first case, into solution that, in place 
•of copper deposits, brass deposits with tones of color varying 
according to the temperature are in a short time obtained. 

According to Darlay's patent, an alkaline copper cyanide 
bath heated to between 185° and 194° F. is to be used, the 
■ electrolyte consisting of: 

Water 1 quart, cupric sulphate 0.35 oz., potassium cyanide 
0.42 oz., caustic soda 0.52 oz. 

When in such formulas the quantity of potassium cyanide 
is given without stating its content in per cent., it would, as a 
rule, be understood to refer to the 98 or 99 per cent, article. 
However, according to experiments made with Bacco's bath, 
with the use of 98 per cent, potassium cyanide, the excess 
would be too large, and it may be supposed that Darlay's 
formula refers to 60 per cent, potassium cyanide. 

However, in this respect, the patent specification does not 
agree with the facts. For instance, the content of potassium 
cyanide "is exactly to be adhered to" in order to prevent 
a deposit of copper upon the contact-body — an aluminium 



BY CONTACT, BY BOILING, AND BY FRICTION. 497 

basket. However, no matter whether potassium cyanide with 
a content of 60 per cent., or more is used, a heavy deposit of 
copper is always formed upon the aluminium,* and the for- 
mation of a deposit of copper upon the objects is not in the 
least dependent upon adhering exactly to the quantity of 
potassium cyanide given. 

The chemical process of Darlay's formula consists therefore 
in the conversion of cupric sulphate and potassium cyanide to 
potassium-copper cyanide. With the use of 68 per cent, 
potassium cyanide scarcely any free potassium cyanide is 
contained in the bath, while with 98 per cent, potassium 
cyanide, free potassium cyanide remains in the bath. If, now 
"the accurately-fixed content of potassium cyanide" in Dar- 
lay's formula refers to the 60 per cent, article, we come back 
to Bacco's formula, in which just enough potassium cyanide 
is added to the cupric sulphate solution to redissolve the sep- 
arated cupro-cupric cyanide, a content of free potassium 
cyanide being avoided. Bacco effects alkalinity by ammonia 
and Darlay by caustic soda. From this it will be seen that 
Darlay's formula is very similar to Bacco's, and it is doubtful 
whether a patent-right can be claimed on the substitution of 
caustic soda for ammonia. At any rate, now that Basse and 
Selve's patent has expired, it is obvious that Bacco's bath 
with the use of aluminium-contact can be employed for cop- 
pering by contact without infringing on Darlay's patent. 

The so-called brush-coppering, which has been recommended, 
may here be mentioned. This process may be of practical 
advantage for coppering very large objects which b} 7 another 
method could only be coated with difficulty. The deposit of 
copper is, of course, very thin. The process is executed as 
follows : The utensils required are two vessels of sufficient size, 
each provided with a brush, preferably so wide that the entire 
surface of the object to be treated can be coated with one ap- 

* According to experiments made by Friessner, about 90 per cent, of the metal 
•contained in the bath was deposited upon the contact-body, and only 10 per cent, 
•upon the objects. 

32 



498 ELECTRO-DEPOSITION OF METALS. 

plication. One of the vessels contains a strongly saturated 
solution of caustic soda, and the other a strongly saturated 
solution of blue vitriol. For coppering, the well-cleansed 
object is first uniformly coated with a brushful of the caustic 
soda solution, and then also with a brushful of the blue vitriol 
solution. A quite thick film of copper is immediately de- 
posited upon the object. Care must be had not to have the 
brush too full, and not to touch the places once gone over the 
second time, as otherwise the layer of copper does not adhere 
firmly. 

Many iron and steel objects, for instance, wire, springs, etc.,. 
are provided with a thin film of copper in order to give them 
a more pleasing appearance. For this purpose a copper solu- 
tion of 10 quarts of water, If ozs. of blue vitriol, and If ozs. 
of pure concentrated sulphuric acid may be used. Dip the 
iron or steel objects, previously freed from grease and oxide,, 
for a moment in the solution, moving them constantly to and 
fro ; then rinse them immediately in ample water, and dry. 
By keeping the articles too long in the solution the copper 
separates in a pulverulent form, and does not adhere. 

Steel pens, needles' eyes, etc., may be coppered by diluting the 
copper solution just mentioned with double the quantity of 
water, moistening sawdust with the solution, and revolving 
the latter, together with the objects to be coppered, in a wooden 
tumbling barrel. 

Brassing by Contact. 

Some older authors have given formulas for baths for 
brassing by contact, but the results obtained are not very 
satisfactory. 

Darlay has patented the bath given below. It is brought 
into commerce under the name of autovolt brass bath, and yields- 
thin brass deposits of an agreeable color and good luster : 

Water 1 quart, cupric sulphate 0.14 oz., zinc sulphate 0.35- 
oz., potassium cyanide 0.44 oz., caustic soda 0.52 oz. 

On testing this formula it was found that with the use of 



BY CONTACT, BY BOILING, AND BY FRICTION. 499 

98 per cent, potassium cyanide the bath yielded no deposit, 
one being, however, obtained with the 60 per cent, article. 
What has been said in reference to the autovolt copper bath 
applies also to the brass bath. 

As previously mentioned, deposits produced by contact can- 
not be obtained of any thickness, the contact-metal soon be- 
coming covered with a deposit when the process comes to a 
standstill. Aluminium, to be sure, relinquishes the deposited 
metal in coherent lamina?, this being promoted by the heavy 
evolution of hydrogen. However, it shows also how large 
are the quantities of metal which are deposited upon the alu- 
minium, and that deposition by contact is consequently con- 
nected with a waste of metallic salts, which considerably 
increases the cost of manufacture. For removing the deposit 
upon the aluminium body, mixtures of nitric and sulphuric 
acids have to be used, so that, in addition to the loss of metal, 
there is a considerable consumption of acids. 

Iron objects brassed in the above-mentioned baths have, to 
be sure, quite a neat appearance, but soon commence to rust, 
and for this reason cannot serve as substitutes for objects 
thickly brassed by means of an external source of current. 

Silvering by Contact, Immersion and Friction. 

For contact-silvering of copper and brass objects the follow- 
ing bath may be used : 

Water 1 quart, crystallized silver nitrate 0.52 oz., 60 per 
cent, potassium cyanide 1.4 ozs. 

The bath is to be somewhat heated, so that deposition does 
not take place too slowly. Zinc is very suitable for a contact- 
metal, but to avoid formation of stains, the contact-points 
have to be frequently changed. 

If iron articles are to be silvered, it is recommended to add 
to the bath, heated to between 176° and 194° F., about 0.28 
to 0.35 oz. of caustic soda, and to use an aluminium contact ; 
for smaller objects in quantities an aluminium basket. It is 
of greater advantage, in all cases, first to brass or copper the 
iron objects. 



500 ELECTRO-DEPOSITION OF METALS. 

According to Darlay's German patent, 128,318, the follow- 
ing baths serve for silvering by contact with aluminium : 

Water 1 liter (2.11 pints), silver nitrate 30 grammes (0.7 
oz.), potassium cyanide 10 grammes (0.35 oz.), caustic potash 
4 grammes (0.14 oz.). 

Information regarding the content in percent, for potassium 
cyanide is wanting. Besides, the quantity of potassium cya- 
nide in proportion to silver nitrate is too low, which may be 
due to a typographical error, and it may be supposed that the 
formula for a 25-liter bath, as given in the patent specifica- 
tion, should read 0.05 kilogramme of silver nitrate instead of 
0.5 kilogramme. This, calculated to 1 liter, gives 2 grammes 
instead of 20 grammes of silver nitrate. 

For silvering iron and steel in hot baths : 

Water 1 quart, silver nitrate 0.44 oz., potassium cyanide 
4.4 ozs., sodium phosphate 0.88 oz. 

The object of the sodium phosphate here is not to prevent 
the adhesion of the metal deposited upon the contact metal, 
which is to be effected by the excess of potassium cyanide. 
However, in experiments made with this bath, more silver 
was deposited upon the contact-body than upon the objects. 

Silvering by immei'sion. For silvering coppered or brassed 
objects by immersion, the following solution may be used : 

Water 1 quart, silver nitrate 0.35 oz., 98 per cent, potassium 
cyanide 1.23 ozs. 

To prepare the bath dissolve the silver salt in 1 pint of the 
water, then the potassium cyanide in the remaining pint of 
water, and mix the two solutions. The bath is heated in a 
porcelain or enameled iron vessel to between 176° and 194° F., 
and the thoroughly cleansed and pickled objects are immersed 
in it until uniformly coated, previous quicking being not re- 
quired. The deposit is lustrous if the articles are left but a 
short time in the bath, but becomes dull when they remain 
longer. In the first case the deposit is a mere film, and, while 
it is somewhat thicker in the latter, it can under no circum- 
stances be called solid. The thickness of the deposit does not 



BY CONTACT, BY BOILING, AND BY FRICTION. 501 

increase by continued action, as much metal being dissolved 
as silver is deposited, and the silver deposit prevents a further 
dissolving effect upon the basis metal. 

The bath gradually works less effectively, and finally ceases 
to silver, when its action may be restored by the addition of 
2f to 5J drachms of potassium cyanide per quart. Should 
this prove ineffectual, the content of silver is nearly ex- 
hausted, and the bath is evaporated to dryness, and the resi- 
due added to the silver waste. Frequent refreshing of the 
bath with silver salt cannot be recommended, the silvering 
always turning out best in a fresh bath. 

A solution of nitrate of silver in sodium sulphite is, accord- 
ing to Roseleur, very suitable for silvering by immersion. 
The solution is prepared by pouring into moderately concen- 
trated solution of sodium phosphite, while constantly stirring, 
solution of a silver salt until the precipitate of silver sulphide 
formed begins to be dissolved with difficulty. The bath can 
be used cold or warm, fresh solution of silver being added 
when it commences to lose its effect. If, however, the bath is 
not capable of dissolving the silver sulphide formed, concen- 
trated solution of sodium sulphite has to be added. 

For the preparation of the solution of sodium sulphite, 
Roseleur recommends the following method : 

Into a tall vessel of glass or porcelain (Fig. 134) introduce 
5 quarts of water and 4 pounds of crystallized soda, after 
pouring in mercury about an inch or so deep to prevent the 
glass tube through which the sulphurous acid is introduced 
from being stopped up by crystals. The sulphurous acid is 
evolved by heating copper turnings with concentrated sul- 
phuric acid, washing the gas in a Woulff bottle filled an inch 
or so deep with water, and introducing it into the bottle con- 
taining the soda solution, as shown in the illustration. A 
part of the soda becomes transformed into sodium sulphite, 
which dissolves, and a part is precipitated as carbonate. The 
latter, however, is transformed into sodium sulphite by the 
continuous action of sulphurous acid, and carbonic acid gas 



502 



ELECTRO-DEPOSITION OF METALS. 



escapes with effervescence. When all has become dissolved, 
the introduction of sulphurous acid should be continued until 
the liquid slightly reddens blue litmus paper, when it is set 
aside for 24 hours. At the end of that time a certain quan- 
tity of crystals will be found upon the mercury, and the liquid 
above, more or less colored, constitutes the sodium sulphite of 
the silvering bath. The liquid sodium sulphite thus prepared 
should be stirred with a glass rod, to eliminate the carbonic 
acid which may still remain in it. The liquid should then 
be again tested with blue litmus paper, and if the latter is 
strongly reddened, carbonate of soda is cautiously added, little 

Fig. 134. 




by little, in order to neutralize the excess of sulphurous acid. 
On the other hand, if red litmus paper becomes blue, too 
much alkali is present, and more sulphurous acid gas must be 
passed through the liquid, which is in the best condition for 
our work when it turns litmus paper violet or slightly red. 
The solution should mark from 22° to 20° Be., and should 
not come in contact with iron, zinc, tin, or lead. 

As will be seen, this mode of preparing the sodium sulphite 
solution is somewhat troublesome, and it is therefore recom- 
mended to proceed as follows : Prepare a saturated solution of 



BY CONTACT, BY BOILING, AND BY FRICTION. 503 

commercial sodium sulphite. The solution will show an alka- 
line reaction, the commercial salt frequently containing some 
sodium carbonate. To this solution add, while stirring, solu- 
tion of bisulphite of sodium saturated at 122° F., until blue 
litmus paper is slightly reddened. Then add to this solution 
concentrated solution of nitrate of silver until the flakes of 
silver sulphide separated begin to dissolve with difficulty. 

The immersion-bath, prepared according to one or the other 
method, works well, the silvering produced having a beautiful 
luster, such as is desirable for many cheap articles. If the 
articles are allowed to remain •for a longer time in the bath, a 
mat deposit is obtained. For bright silvering, the bath 
should always be used cold. It must further be protected as 
much as possible from the light, otherwise decomposition 
gradually takes place. 

According to Dr. Ebermayer, a silver immersion-bath for 
bright silvering is prepared as follows: Dissolve 1.12 ozs. of 
nitrate of silver in water, and precipitate the solution with 
caustic potash. Thoroughly wash the silver oxide which is 
precipitated, and dissolve it in 1 quart of water which con- 
tains 3.52 ozs. of potassium cyanide in solution, and finally 
dilute the whole with one quart more water. For silvering, 
the bath is heated to the boiling-point, and the silver with- 
drawn may be replaced by the addition of moist silver oxide 
as long as complete solution takes place. When the silvering 
is no longer beautiful and of a pure white color, the bath is 
useless, and is then evaporated. Experiments with a bath 
prepared according to the above directions were never quite 
satisfactory. Better results were, however, obtained by dilu- 
ting the bath with 3 to 4 quarts of water and using it without 
heating. It then yielded very nice, lustrous silvering. 

The process of coating with a thin film, or rather whitening, 
with silver, small articles, such as hooks and eyes, pins, etc., 
differs from the above-described immersion method, which 
effects the silvering in a few seconds, in that the articles re- 
quire to be boiled for a longer time. The process is as follows : 



504 ELECTRO-DEPOSITION OF METALS. 

Prepare a paste from 0.88 oz. of silver nitrate precipitated 
as silver chloride, cream of tartar 44 ozs. and a like quantity 
of common salt, by precipitating the silver nitrate with hydro- 
chloric acid, washing the chloride of silver and mixing it with 
the above-mentioned quantities of cream of tartar and common 
salt, and sufficient water to a paste, which is kept in a dark 
glass vessel to prevent the chloride of silver from being decom- 
posed by the light. Small articles of copper or brass are first 
freed from grease and pickled. Then heat in an enameled 
kettle 3 to 5 quarts of rain-water to the boiling-point ; add 2 
or 3 heaping teaspoonfuls of the above-mentioned paste, and 
bring the metallic objects contained in a stoneware basket into 
the bath, and stir them diligently with a rod of glass or wood. 
Before placing a fresh lot of articles in the bath, additional sil- 
ver paste must be added. If finally the bath acquires a green- 
ish color, caused by dissolved copper, it is no longer suitable 
for the purpose, and is then evaporated and added to the sil- 
ver residues. 

Cold silvering with paste. — In this process an argentiferous- 
paste, composed as given below, is rubbed, by means of the- 
thumb, a piece of soft leather, or rag, upon the cleansed and 
pickled metallic surface (copper, brass, or other alloys of cop- 
per) until it is entirely silvered. The paste may also be rubbed 
in a mortar with some water to a uniformly thin-fluid mass, and 
applied with a brush to the surface to be silvered. By allow, 
ing the paste to dry naturally, or with the aid of a gentle 
heat, the silvering appears. The application of the paste by 
means of a brush is chiefly made use of for decorating with 
silver, articles thinly gilded b}' immersion. For articles not 
gilded, the above-mentioned rubbing-on of the stiff paste is to 
be preferred. 

Composition of argentiferous paste. — I. Silver in the form of 
freshly precipitated chloride of silver,* 0.352 oz.. common 
salt 0.35 oz., potash 0.7 oz., whiting 0.52 oz. and water a suffi- 
cient quantity to form the ingredients into a stiff paste. 

II. Silver in the form of freshly precipitated chloride of sil- 



BY CONTACT, BY BOILING, AND BY FRICTION. 505 

ver * 0.35 oz., potassium cyanide 1.05 ozs., sufficient water to- 
dissolve these two ingredients to a clear solution, and enough 
whiting to form the whole into a stiff paste. This paste is 
also excellent for polishing tarnished silver ; it is, however, 
poisonous. 

The following non-poisonous composition does excellent 
service: Silver in the form of chloride of silver 0.35 oz., 
cream of tartar 0.7 oz., common salt 0.7 oz., and sufficient 
water to form the mixture of the ingredients into a stiff paste. 

Another composition is as follows : Chloride of silver 1 part, 
pearl ash 3, common salt 1J, whiting 1, and sufficient water 
to form a paste. Apply the latter to the metal to be silvered 
and rub with a piece of soft leather. When the metal is sil- 
vered, wash in water, to which a small quantity of washing 
soda has been added. 

Graining. — In gilding parts of watches, gold is seldom di- 
rectly applied upon the copper; there is generally a prelim- 
inary operation called graining, by which a grained and 
slightly dead appearance is given to the articles. Marks of 
the file are obliterated b}' rubbing upon a whetstone, and 
lastly upon an oil stone. Any oil or grease is removed hj 
boiling the parts for a few minutes in a solution of 10 parts 
of caustic soda or potash in 100 of water, which should wet 
them entirely if all the oil has been removed. The articles 
being threaded upon a brass wire, cleanse them rapidly in the 
acid mixture for a bright luster, and dry them carefully in 
white wood sawdust. The pieces are fastened upon the even 
side of a block of cork by brass pins with flat heads. The- 
parts are then thoroughly rubbed over with a brush entirely 
free from grease, and dipped into a paste of water and very 
fine pumice-stone powder. Move the brush in circles, in order 
not to rub one side more than the other ; thoroughly rinse in 
cold water, and no particle of pumice-stone should remain 
upon the pieces of cork. Next place the cork and the pieces- 

* From 0.56 oz. of nitrate of silver. 



506 ELECTRO-DEPOSITION OF METALS. 

in a weak mercurial solution, composed of water 1\ gallons, 
nitrate or binoxide of mercury T V oz., sulphuric acid \ oz., 
which slightly whitens the copper. The pieces are passed 
quickly through the solution and then rinsed. This opera- 
tion gives strength to the graining, which without it possesses 
no adherence. 

The following preparations may be used for graining : I. 
Silver in impalpable powder 2 ozs., finely-pulverized cream of 
tartar 20 ozs., common salt 4 lbs. II. Silver powder 1 oz., 
cream of tartar 4 to 5 ozs., common salt 13 ozs. III. Silver 
powder, common salt, and cream of tartar, equal parts by 
weight of each. The mixture of the three ingredients must 
be thorough and effected at a moderate and protracted heat. 
The graining is the coarser the more common salt there is in 
the mixture, and it is the finer and more condensed as the pro- 
portion of cream of tartar is greater, but it is then more diffi- 
cult to scratch-brush. The silver powder is obtained as follows: 
Dissolve in a glass or porcelain vessel § oz. of crystallized 
nitrate of silver in 1\ gallons of distilled water, and place 5 
or 6 ribbands of cleansed copper, f inch wide, in the solution. 
These ribbands should be long enough to allow of a portion of 
them being above the liquid. The whole is kept in a dark 
place, and from time to time stirred with the copper ribbands. 
This motion is sufficient to loosen the deposited silver, and 
present fresh surfaces to the action of the liquor. When no 
more silver deposits on the copper the operation is complete, 
•and there remains a blue solution of nitrate of copper. The 
silver powder is washed by decantation or upon a filter until 
there remains nothing of the copper solution. 

For the purpose of graining, a thin paste is made of one of 
the above mixtures and water, and spread by means of a spatula 
oipon the watch parts held upon the cork. The cork itself is 
placed upon an earthenware dish, to which a rotating move- 
ment is imparted by the left hand. An oval brush with close 
bristles, held in the right hand, rubs the watch parts in every 
direction, but always with a rotary motion. A new quantity 



BY CONTACT, BY BOILING, AND BY FRICTION. 507 

of paste is added two or three times and rubbed in the manner 
indicated. The more the brush and cork are turned, the 
rounder becomes the grain, which is a good quality, and the 
more paste added, the larger the grain. When the desired 
grain is obtained, the pieces are washed and scratch-brushed. 
The brushes employed are of brass wire, as fine as hair, and 
very stiff and springy. It is necessary to anneal them upon 
an even fire to different degrees ; one soft or half annealed for 
the first operation or uncovering the grain ; one harder for 
bringing up the luster ; and one very soft or fully annealed, 
used before gilding for removing any marks which may have 
been made by the preceding tool, and for scratch-brushing 
after gilding, which, like the graining, must be done by giv- 
ing a rotary motion to the tool. If it happens that the same 
watch part is. composed of copper and steel, the latter metal 
requires to be preserved against the action of the cleansing 
acids and of the graining mixture by a composition called 
resist. This consists in covering the pinions and other steel 
parts with a fatty composition which is sufficiently hard to 
resist the tearing action of the bristle and wire brushes, and 
insoluble in the alkalies of the gilding bath. A good compo- 
sition is : Yellow wax, 2 parts by weight ; translucent rosin, 
3J ; extra-fine red sealing-wax, 1J ; polishing rouge, 1. Melt 
the rosin and sealing-wax in a porcelain dish, upon a water- 
bath, and afterwards add the yellow wax. When the whole 
is thoroughly fluid, gradually add the rouge and stir with a 
wooden or glass rod, withdraw the heat, but continue the stir- 
ring until the mixture becomes solid, otherwise all the rouge 
will fall to the bottom. The flat parts to receive this resist 
are slightly heated, and then covered with the mixture, which 
melts and is easily spread. For covering steel pinions employ 
a small gouge of copper or brass fixed to a wooden handle. 
The metallic part of the gouge is heated upon an alcohol 
lamp and a small quantity of resist is taken with it. The 
composition soon melts, and by turning the tool around, the 
steel pinion thus becomes coated. Use a scratch-brush with 



508 ELECTRO-DEPOSITION OF METALS. 

long wires, and their flexibilit} 7 prevents the removal of the 
composition. When the resist is to be removed after gilding, 
put the parts into warm oil or tepid turpentine, then in a very 
hot soap-water or alkaline solution ; and, lastly, into fresh 
water. Scratch-brush and dry in warm, white wood saw-dust. 
The holes of the pinions are cleansed and polished with small 
pieces of, very white, soft wood, the friction of which is suffi- 
cient to restore the primitive luster. The gilding of parts of 
copper and steel requires the greatest care, as the slightest rust 
destroys their future usefulness. Should some gold deposit 
upon the steel, it should be removed by rubbing with a piece 
of wood and impalpable pumice dust, tin putty, or rouge. 

The gilding of the grained watch parts is effected in a bath 
prepared according to formula I or III, given under "Deposi- 
tion of Gold." 

Gilding by Contact, by Immersion, and by Friction. 

For contact-gilding by touching with zinc, formulas I, II, 
IV and V, given in Chapter IX " Deposition of Gold " may 
be used, IV and V being especially suitable, if the addition 
of potassium cyanide is somewhat increased and the baths are 
sufficiently heated. 

A contact gold bath prepared with yellow prussiate of 
potash according to the following formula also yields a good 
deposit. 

I. Fine gold as chloride of gold 54 grains, yellow T prussiate 
of potash 1 oz., potash 1 oz., common salt 1 oz., water 1 quart. 

The bath is prepared as given for formula III under 
" Deposition of Gold." For use, heat it to boiling. 

II. Chemically pure crystallized sodium phosphate 2.11 ozs. r 
neutral crystallized sodium sulphite 0.35 oz., potassium cya- 
nide 0.28 oz., fine gold (as chloride) 15.43 grains, water 1 
quart. 

The bath is prepared as given for formula V under " Depo- 
sition of Gold." Temperature for contact-gilding 185° to 
194° F. If red gilding is to be effected in this bath a corres- 



BY CONTACT, BY BOILING, AND BY FRICTION. 509 

ponding addition of potassium-copper cyanide has to be made, 
1\ grains sufficing for paler red, while 15 grains have to be 
added for redder tones. 

Gilding by contact is done the same way as silvering by 
■contact. The points of contact must be frequently changed, 
since in the gold bath intense stains are still more readily 
formed than in the silver bath. 

Gilding by immersion {without battery or contact). The fol- 
lowing two formulas have proved very useful : 

I. Crystallized sodium pyrophosphate 2.82 ozs., 12 per cent, 
prussic acid 4.51 drachms, crystallized chloride of gold 1.12 
drachms, water 1 quart. Heat the bath to the boiling-point, 
and immerse the pickled objects of copper or its alloys, mov- 
ing them constantly until gilded. Iron, steel, tin, and zinc 
should be previously coppered, coating the objects with mer- 
cury (quicking) being entirely superfluous. 

All gold baths prepared with sodium pyrophosphate, when 
fresh, give rapid and beautiful results, but they have the dis- 
advantage of rapidty decomposing, and consequently can 
seldom be completely exhausted. In this respect the follow- 
ing formula answers much better. 

II. Crystallized sodium phosphate 2.82 drachms, chem- 
ically pure caustic potash 1.69 drachms, chloride of gold 0.56 
drachm, 98 per cent, potassium cyanide 9.03 drachms, water 
1 quart. Dissolve the sodium phosphate and caustic potash 
in | of the water, and the potassium cyanide and chloride of 
gold in the remaining J, and mix both solutions. Heat the 
solution to the boiling-point. This bath can be almost entirely 
exhausted, as it is not decomposed by keeping. Should the 
bath become weak, add about 2f drachms of potassium cya- 
nide, and use it for preliminary dipping until no more gold 
is reduced. To complete gilding, the objects subjected to such 
preliminary dipping are then immersed for a few seconds in a 
freshly prepared bath of the composition given above. 

The bath prepared according to formula II is also very 
suitable for contact gilding. 



510 ELECTRO-DEPOSITION OF METALS. 

The layer of gold produced by immersion is in all cases 
very thin, since only as much gold is deposited as corresponds 
to the quantity of basis-metal dissolved. For heavier gilding 
by this process the action of zinc or aluminium contact will 
have to be employed as auxiliary means. 

Gilding by friction. This process is variously termed gilding 
with the rag, with the thumb, with the cork. It is chiefly em- 
ployed upon silver, though sometimes also upon brass and 
copper. The operation is as follows: Dissolve 1.12 to 1.69 
drachms of chloride of gold in as little water as possible, to 
which has previously been added 0.56 drachm of saltpetre. 
Dip in this solution small linen rags, and, after allowing them 
to drain off, dry them in a dark place. These rags saturated 
with gold solution are then charred to tinder at. not too great 
a heat, whereby the chloride of gold is reduced, partially to 
protochloride and partial^ to finely-divided metallic gold. 
This tinder is then rubbed in a porcelain mortar to a fine, 
uniform powder. 

To gild with this powder, dip into it a charred cork moist- 
ened with vinegar or salt water and rub, with not too gentle a 
pressure, the surface of the article to be gilded, which must 
be previously cleansed from adhering grease. The thumb of 
the hand may be used in place of the cork, but in both cases 
care must be had not to moisten it too'much, as otherwise the 
powder takes badly. After gilding, the surface may be care- 
fully burnished. 

Reddish gilding by friction is obtained by adding about 8 
grains of cupric nitrate to the gold solution. 

For gilding by friction, a solution of chloride of gold in an 
excess of potassium cyanide may also be used, after thicken- 
ing the solution to a paste by rubbing in whiting. The paste 
is applied to the previously zincked metals by means of a cork, 
a piece of leather or a brush. Martin and Pe} r raud, the orig- 
inators of this method, describe the operation as follows : 
Articles of other metals than zinc are placed in a bath consist- 
ing of concentrated solution of ammonium chloride, in which 



BY CONTACT, BY BOILING, AND BY FRICTION. 511 

has been placed a quantity of granulated zinc. The articles 
are allowed to boil a few minutes, whereby they acquire a 
coating of zinc. For the preparation of the gilding composi- 
tion, dissolve 11.28 drachms of chloride of gold in a like 
quantity of water, and add a solution of 2.11 ozs. of potassium 
cyanide in as little water as possible (about 2.8 ozs.). Of this 
solution add so much to a mixture of 3.52 ozs. of fine whiting 
and 2.82 drachms of pulverized tartar that a paste is formed 
which can be readily applied with a brush to the article to be 
gilded. When the article is coated, heat it to between 140° 
and 158° F. After removing the dry paste by washing, the 
gilding appears and can be polished with the burnisher. 

Platinizing by contact. 

Though a thick deposit cannot be produced by the contact- 
process, Fehling's directions may here be mentioned as suit- 
able for giving a thin coat of platinum to fancy articles. He 
recommends a solution of 0.35 oz. of chloride of platinum and 
7 ozs. of common salt in 1 quart of water, which is made alka- 
line by the addition of a small quantity of soda lye, and for 
use heated to the boiling-point. 

If larger articles are to be platinized by contact, free them 
from grease, and after pickling, and if necessary, coppering, 
wrap them round with zinc wire, or place them upon a bright 
zinc sheet, and introduce them into the heated bath. All the 
remaining manipulations are the same as in other contact- 
processes. 

Tinning by Contact and by Boiling. 

For tinning by zinc-contact in the boiling tin bath, the follow- 
ing solutions are suitable : 

According to Gerhold : Pulverized tartar and alum, of each 
3.5 ozs., fused stannous chloride 0.88 oz., rain-water 10 quarts. 

According to Roseleur : Potassium pyrophosphate 7 ozs., 
crystallized stannous chloride (tin-salt) 0.38 oz., fused stan- 
nous chloride 2.8 ozs., rain-water 10 quarts. 



512 ELECTRO-DEPOSITION OF METALS. 

It might be advisable to increase the content of potassium 
pyrophosphate, and to add about 0.7 oz. of caustic soda. 

According to Roseleur by immersion : 

Potassium pyrophosphate 5.6 ozs., fused stannous chloride 
-1.23 ozs., rain-water 10 quarts. 

For tinning by contact, heat the bath to boiling and suspend 
the clean and pickled objects in contact with pieces of zinc 
or, better, wrapped around with zinc wire spirals, care being 
had from time to time to shift them about to prevent staining. 
Large baths which cannot be readily heated are worked cold, 
the objects being covered with a large zinc plate. In the cold 
bath the formation of the tin deposit requires, of course, a 
longer time. By using the electric current the deposit can be 
made as heavy as desired. By immersion in the bath pre- 
pared according to the last formula, zinc can only be coated 
with a very thin film of tin. 

For tinning by contact in a cold bath, Zilk'en has patented 
the following solution : Dissolve with the aid of heat in 100 
quarts of water, tin-salt 7 to 10.5 ozs., pulverized alum 10.5 
ozs., common salt 15f ozs., and pulverized tartar 7, ozs. The 
cold solution forms the tin bath. The objects to be tinned 
are to be wrapped round with strips of zinc. Duration of the 
process, 8 to 10 hours. 

Darlay uses for a cold tin bath with aluminium-contact : 

Water 10 quarts, stannous chloride 1.05 ozs., potassium 
cyanide 1.41 ozs., caustic soda 1.76 ozs. 

It might be advisable to heat the bath to at least between 
113° and 122° F. For a hot tin bath Darlay uses : 

Water 10 quarts, stannous chloride 0.88 oz., potassium cya- 
nide 10.58 ozs., caustic soda 0.88 oz., sodium pyrophosphate 
■8.8 ozs. 

The contact-body cannot be kept free from deposit by the 
addition of potassium cyanide, and tinning is effected as well 
without as with the addition of potassium cyanide. 

Tinning solution for iron and steel articles. Crystallized 
ammonium-alum 7 ozs., crystallized stannous chloride 2.8 



BY CONTACT, BY BOILING, AND BY FRICTION. 513 

drachms, fused stannous chloride 2.8 drachms, rain-water 10 
quarts. Dissolve the ammonium-alum in the hot water, and 
when dissolved add the tin-salts. The bath is to be used boil- 
ing hot and kept at its original strength by an occasional ad- 
dition of tin-salt. The clean and pickled iron objects, after 
being immersed in the bath, become in a few seconds coated 
with a firmly-adhering film of tin of a dead, white color, which 
may be polished by scratch-brushing, or scouring with saw- 
dust in the tumbling barrel. Tinning by boiling in the above 
betth is the most suitable preparation for iron and steel objects 
which are finally to be provided with a heavy electro-deposit 
of tin. To insure entire success it is recommended thoroughly 
to scratch-brush the objects after boiling, then to return them 
once more to the bath, and finally to suspend them in a bath 
composed according to formula I, Ila or III, given under 
" Deposition of Tin." 

A tinning solution for small brass and copper articles (pins, 
eyes, hooks, etc.), consists of a boiling solution of: Pulverized 
tartar 3.5 ozs., stannous chloride (tin-salt) 14.11 drachms, 
water 10 quarts. After heating the bath to the boiling-point, 
immerse the objects to be tinned in a tin basket, or in contact 
with pieces of zinc in a stoneware basket. Frequent stirring 
with a tin rod shortens the process. 

A tinning solution highly recommended by Roseleur con- 
sists of : 

Crystallized sodium pyrophosphate 7 ozs., crystallized stan- 
nous chloride 0.7 oz., fused stannous chloride 2.82 ozs., water 
10 quarts. 

The solution is prepared in the same manner as the preced- 
ing one. 

Another solution, given by Bottger, also yields good results : 
Dissolve oxide of tin by boiling with potash lye, and place the 
copper or brass objects to be tinned in the boiling solution in 
contact with tin shavings. 

Eisner's bath yields equally good results. It consists of a so- 
lution of equal parts of tin-salt and common salt in rain-water. 
The manipulation is the same as given above. 
33 



514 ELECTRO-DEPOSITION OF METALS. 

A characteristic method of tinning by Stolba is as follows : 
Prepare a solution of 1.75 ozs. of tin-salt and 5.64 drachms of 
pulverized tartar in one quart of water. Moisten with this so- 
lution a small sponge and dip the latter into pulverulent zinc. 
By then rubbing the thoroughly cleansed and pickled articles 
with the sponge, they immediately become coated with a film 
of tin. To obtain uniform tinning, the sponge must be re- 
peatedly dipped, now into the solution, and then into the zinc- 
powder, and the rubbing continued for a few minutes. 

Zincking by Contact. 

For zincking iron by contact, a concentrated solution of zinc 
chloride and ammonium chloride in water is very suitable. 
The objects are placed in the solution in contact with a large 
zinc surface. 

Darlay (German patent 128319) gives the following bath 
which, with an aluminium contact is claimed to yield a useful 
coating of zinc : 

Water 10 quarts, zinc sulphate 0.35 ozs., potassium cyanide 
1 Oz., caustic soda 5.29 ozs. 

It may be supposed that the bath is to be heated to between 
170° and 194° F., though the patent specification is silent on 
this point. Experiments to obtain, according to these direc- 
tions, a good coating of zinc on iron did not yield satisfactory 
results. 

To coat brass and copper with a bright layer of zinc proceed 
as follows : Boil for several hours commercial zinc-gray, i. e., 
very finely-divided metallic zinc, with concentrated solution 
of caustic soda. Then immerse the articles to be zincked in 
the boiling fluid, when, by continued boiling, they will in a 
short time become coated with a very bright layer of zinc. 
When a copper article thus coated with zinc is carefully 
heated in an oil bath to between 248° and 284° F., the zinc 
alloys with the copper, forming a sort of bronze similar to 
tombac. 



BY CONTACT, BY BOILING, AND BY FRICTION. 515 

Depositions of Antimony and of Arsenic by Immersion. 

A heated solution of chloride of antimony in hydrochloric 
acid — liquor stibii chlorati of commerce — deposits upon brass 
objects immersed in it a coating of antimony of a steel-gray 
color inclining to bluish. 

A purer steel-gray color is obtained with the use of a hot 
solution of arsenious chloride in water. 



CHAPTER XIV. 



COLORING OF METALS. 



Metal coloring and bronzing is an important branch of 
the metal industry, its object being, on the one hand, to em- 
bellish the original metallic surface and, on the other, to 
protect it from the influence of atmospheric air, moisture, 
various gases, etc. Although, strictly speaking, these opera- 
tions do not form a part of a work on the electro-deposition 
of metals and cannot be adequately treated within the limits 
of a chapter, a few methods and approved formulas will here 
be given since the electro-plater is frequently forced to make 
use of one or the other method to furnish basis-metals or 
electro-deposits in certain shades of colors demanded by 
customers. 

Metal coloring may be effected by electrolytic, chemical 
and mechanical means. Methods of coloring electrolytically 
have been given under Deposition of Nickel (black nickel- 
ling), and under Deposition of Antimony and Arsenic. 

Mechanical methods of coloring require the use of pigments, 
bronze powders, varnishes, etc. and cannot be here fully de- 
scribed. To the electro-plater the most important of these 
operations is lacquering which will be described in the next 
chapter. 

Attention will here be given chiefly to coloring metals by 
chemical means. 

The practice of coloring metals requires considerable talent 
for observation and a certain knowledge of the behavior of 
metals or metallic alloys towards the chemical substances 
used. 

Especially in coloring alloys, for instance, brass, their per- 

(516) 



COLORING OP METALS. 517 

rentage composition makes a difference, and patinas can be 
produced upon a brass richer in zinc, which cannot be ob- 
tained upon an alloy richer in copper. Hence instructions 
for patinizing have to be changed in one or the other direc- 
tion, and this problem cannot be readily solved without a 
certain chemical knowledge. The temperature of the solu- 
tions used is also of great importance, and the directions given 
in this respect must be accurately observed. 

1. Coloring copper. — With the use of chemicals nearly all 
colors can be produced upon copper, as well as upon other 
metals and alloys, by first coating them electrolytically with 
copper and afterwards coloring the deposit. For the produc- 
tion of yellow and brown, alkaline sulphides are, for instance, 
used, for green, copper salts, for black, metallic silver, bis- 
muth, platinum, etc. 

All shades from the pale red of copper to a dark chestnut 
brown can be obtained by superficial oxidation of the copper. 
For small objects it suffices to heat them uniformly over an 
alcohol flame. With larger objects a more uniform result is 
obtained by heating them in oxidizing fluids or brushing them 
over with an oxidizing paste, the best results being obtained 
with a paste prepared, according to the darker or lighter shades 
desired, from 2 parts of ferric oxide and 1 part of black-lead, 
or 1 part each of ferric oxide and black-lead, with alcohol or 
water. Apply the paste as uniformly as possible with a 
brush, and place the object in a warm place (oven or drying 
chamber). The darker the color is to be the higher the tem- 
perature must be, and the longer it must act upon the object. 
When sufficiently heated, the dry powder is removed by brush- 
ing with a soft brush, and the manipulation repeated if the 
object does not show a sufficiently dark tone. Finally the 
object is rubbed with a soft linen rag moistened with alcohol, 
or brushed with a soft brush and a few drops of alcohol until 
completely dry, and then with a brush previously rubbed 
upon pure wax. The more or less dark shade produced in 
this manner is very warm, and resists the action of the air. 



518 ELECTRO-DEPOSITION OF METALS. 

Brown color on copper. — Apply to the thoroughly cleansed 
object a paste made of verdigris 3 parts, ferric oxide 3, sal 
ammoniac 1, and sufficient vinegar and heat until the paste 
turns black, then wash and dry the object. By the addition 
of some blue vitriol to the paste the color may be darkened to 
chestnut-brown. 

A brown layer of cuprous oxide on copper is produced as fol" 
lows : After polishing the articles with pumice powder apply 
with a brush a paste made of verdigris 4 parts, ferric oxide 4, 
finely rasped horn shavings 1, and a small quantity of vinegar. 
Dry, heat over a coal fire, wash, and smooth with the polish- 
ing stone. 

A brown color is also obtained by brushing to dryness with 
a hot solution of 1 part of potassium nitrate, 1 of common 
salt, 2 of ammonium chloride, and 1 of liquid ammonia in 
95 of vinegar. A warmer tone is, however, produced by the 
method introduced in the Paris Mint, which is as follows : 
Powder and mix intimately equal parts of verdigris and sal 
ammoniac. Take a heaping tablespoonful of this mixture 
and boil it with water in a copper kettle for about twenty 
minutes, and then pour off the clear fluid. To give copper 
objects a bronze-like color with this fluid, pour part of it into 
a copper pan ; place the objects separately in it upon pieces 
of wood or glass, so that they do not touch each other, or come 
in contact with the copper pan, and then boil them in the 
liquid for a quarter of an hour. Then take the objects from 
the solution, rub them dry with a linen cloth, and brush them 
with a waxed brush. 

A beautiful and uniform brown tone on copper is produced as 
follows : Place the articles, previously freed from grease and 
pickled, in a solution of 5£ ozs. of copper sulphate, and 2f ozs. 
potassium chloride heated to 140° F. until the desired tone is 
produced. Then brush with a soft brass-wire brush, rinse 
again for a short time in the pickle, and finally wipe dry 
with a soft cloth. 

Brown of various shades on copper is produced as follows : 



COLORING OF METALS. 519 

Bring the objects previously cleansed and pickled into a solu- 
tion of liver of sulphur 1£ ozs., or a solution of trichloride of 
antimony (butter of antimony) 1| ozs. in water 1 quart. 
When the desired tone is produced, rinse the objects thor- 
oughly in water and dry. The shade of the color may be 
varied by the concentration of the bath as well as by the 
length of time of its action. The color is finally fixed by 
rubbing with a rag saturated with oil varnish or by rubbing 
heated wax upon the object. 

A beautiful brown on copper by the so-called Chinese process 
is produced as follows : Crystallized verdigris 2 parts, cinnabar 
2, ammonium chloride 5, finely powdered alum 5, intimately 
mixed and made into a thin paste with water or wine vinegar. 
Apply this paste with a brush to the polished surfaces. Then 
heat uniformly over a coal fire and when cold wash carefully 
with water. By the addition of copper sulphate a color shad- 
ing more into chestnut-brown is obtained, and by the addition 
of borax one shading more into yellow. 

Gold-yellow on copper. Treat the objects with a hot solution 
diluted with water, of mercury 10 parts and zinc 1 part in 
hydrochloric acid, to which some pulverized tartar has been 
added. 

According to Manduit, copper and coppered articles may 
be bronzed by brushing with a mixture of castor oil 20 parts, 
alcohol 80, soft soap 40, and water 40. This mixture pro- 
duces tones from bronze Barbedienne to antique green patina, 
according to the duration of the action. After 24 hours the 
article treated shows a beautiful bronze, but when the mixture 
is allowed to act for a greater length of time the tone is 
changed and several different shades of great beauty can be 
obtained. After rinsing, dry in hot sawdust, and lacquer 
with colorless spirit lacquer. 

Yellowish-brown on copper is produced by boiling the objects 
in a saturated solution of potassium chloride and ammonium 
nitrate. By heating the objects after drying them, a more 
reddish-brown color is obtained. 



520 ELECTRO-DEPOSITION OF METALS. 

Dark brown to black on copper is obtained by dissolving 
nitrates of bismuth, copper, silver or cupriferous silver in 
water and adding some nitric acid. Copper to which such a 
fluid has been applied is, when heated, colored brown with 
the use of bismuth, and black with the use of copper and sil- 
ver salts. Very dark Slack is produced by placing the objects 
for half an hour over a vessel containing a saturated solution 
of liver of sulphur to which some hydrochloric acid has been 
added. The luster may be increased by rubbing with a 
woolen cloth and a waxed brush. 

Bed to violet shades on copper articles. According to a pro- 
cess patented in Germany by M. Mayer, the highly polished 
copper article is electrolytically provided with a thin deposit 
of arsenic or antimony. For the preparation of the bath, solu- 
tion of an antimony or arsenic salt is poured into a ferric 
chloride solution till the precipitate formed redissolves. A 
sheet of iron may serve as anode. The articles thus treated 
are then heated to cherry red and again polished. It is 
claimed that the electro-deposit as a carrier of oxygen effects a 
uniform oxidation of the copper underneath, but at the same 
time prevents it from becoming too highly oxidized so that 
by heating a layer of oxide is chiefly formed. The coating 
thus obtained shows red to violet shades, adheres firmly and 
resists physical as well as chemical influences. 

Copper is colored blue-black by dipping the object in a hot 
solution of 11^ drachms of liver of sulphur in 1 quart of water, 
moving it constantly. Blue gray shades are obtained with 
more dilute solutions. It is difficult to give definite directions 
as to the length of time the solution should be allowed to act, 
since this depends on its temperature and concentration. 
With some experience the correct treatment, however, will 
soon be learned. 

The so-called cuivre-fume is produced by coloring the copper 
or coppered objects blue-black with solution of liver of sulphur, 
then rinsing, and finally scratch-brushing them, whereby the 
shade becomes somewhat lighter. From raised portions which 



COLORING OF METALS. 521 

are not to be dark, but are to show the color of copper, the 
coloration is removed by polishing upon a felt wheel or bob. 

Black color upon copper is produced by a heated pickle of 2 
parts of arsenious acid, 4 of concentrated muriatic acid, 1 of 
sulphuric acid of 66° Be., and 24 of water. 

Mat-black on copper. — Brush the object over with a solution 
of 1 part of platinum chloride in 5 of water, or dip it in the 
solution. A similar result is obtained by dipping the copper 
object in a solution of nitrate of copper or of manganese, and 
drjnng over a coal fire. These manipulations are to be re- 
peated until the formation of a uniform mat-black. 

A solution recommended for obtaining a deep black color on 
copper and its alloys is composed as follows : Copper nitrate 
100 parts, water 100 parts. The copper nitrate is dissolved in 
the water, and the article, if large, is painted with it ; if small, 
it may be immersed in the solution. It is then heated over a 
clear coal fire and lightly rubbed. The article is next placed 
in, or painted, with a solution of the following composition : 
Potassium sulphide 10 parts, water 100, hydrochloric acid 5. 

More uniform results, however, are obtained by using a solu- 
tion about three times more dilute than the above, viz.: Cop- 
per nitrate 100 parts, water 300. Small work can be much 
more conveniently treated by immersion in the solution, and 
after draining off, or shaking off the excess of the solution, 
heating the work on a hot plate until the copper salt is de- 
composed into the black copper oxide. It would be difficult 
to heat large articles on a hot plate, but a closed muffle- 
furnace would give better results than an open coal fire. In 
any case heating should not be continued longer than neces- 
sary to produce the change mentioned above. 

Black color on copper, coppered objects and alloys rich in 
copper. For this purpose Dr. Groschuff gives the following 
directions : Heat a suitable quantity of 5 per cent, soda lye in 
a vessel of glass, porcelain, stoneware or enameled iron to 
212° F., add 1 per cent, powdered potassium persulphate and 
immerse the article previously secured to a wire; an evolu- 



522 ELECTRO-DEPOSITION OF METALS. 

tion of oxygen will be perceptible. The article is moved to 
and fro in the hot bath till the black color desired is pro- 
duced which, with smaller articles, is generally the case 
within five minutes. Should the evolution of oxygen cease 
previous to this, add 1 per cent, more of potassium persulphate. 

The article presenting at first a velvety appearance is rinsed 
in cold water, dried with a soft towel and rubbed ; it will then 
be of a deep black color with mat luster. 

The solution may also be used for coloring black a large 
number of alloys with a high percentage of copper. Gen- 
erally speaking, more time is required for coloring alloys 
than copper. 

Patina. This term is applied to the beautiful green colors 
antique statues and other art-works of bronze have acquired 
by long exposure to the action of the oxygen, carbonic acid, 
and moisture of the air, whereby a thin layer of copper car- 
bonate is formed upon them. It has been sought to accelerate 
by chemical means the formation of the patina thus slowly 
produced by the action of time and the term patinizing has 
been applied to the production of such colors. 

Artificial patina. There are numerous directions for the 
production of an artificial patina on metallic objects, and, in 
conformity with the natural principle of formation, the vari- 
ous artificial processes are based upon the slowest possible 
action of the patinizing fluid. 

To avoid stains the surfaces of the metallic objects should 
be as bright as possible, and any adhering grease must first 
be removed by washing with dilute soda lye. The objects are 
then placed, without touching them with the bare hands, on 
the bench or other place where they are to be patinized. 

Patinizing is effected with a dilute solution applied with a 
brush or sponge. After allowing the first application to dry 
at a temperature of about 60° F., the process is several times 
repeated. The composition of the metal to which the patiniz- 
ing fluid is to be applied, exerts an influence upon the forma- 
tion of a patina of good qualit}^, the latter being most readily 



COLORING OF METALS. 523 

formed upon bronze, while copper and brass are more difficult 
to patinize ; alloys containing arsenic easily turn black. 

Donath makes a distinction between acid and alkaline pat- 
inizing fluids. The former contain acetic acid, oxalic acid, 
hydrofluo-silicic acid, and the latter, ammonia, ammonium 
carbonate, etc. Coatings effected with acids require a longer 
time for their formation ; they are in the beginning less crys- 
talline and at first blue-green, later on, of the color of ver- 
digris, but possess less resistance towards water. Coatings 
produced w T ith ammoniacal fluids have a dull, earthy appear- 
ance, and a blue-green to gray-green color. Yellow-green 
tones are obtained by the addition of chlorides — common salt, 
sal ammoniac — to the solution, while copper nitrate or copper 
acetate yield more blue-green colorations. If a yellow-green 
coloration is to be changed into blue-green, only ammonium 
carbonate solution can subsequently be used. 

Imitation of genuine green patina, as well as its rapid forma- 
tion upon objects of copper, and of bronze and brass, is ob- 
tained by repeatedly brushing the objects with solution of 
ammonium chloride in vinegar, the action of the solution 
being accelerated by the addition of verdigris. A solution of 
9 drachms of ammonium chloride and 2J drachms of potas- 
sium binoxalate (salt of sorrel) in 1 quart of vinegar acts still 
better. When the first coating is dry, wash the object, and 
repeat the manipulations, drying and washing after each ap- 
plication, until a green patina is formed. It is best to bring 
the articles after being brushed over with the solution into a 
hermetically closed box, upon the bottom of which a few 
shallow dishes containing very dilute sulphuric or acetic acid 
and a few pieces of marble are placed. Carbonic acid being 
thereby evolved, and the air in the box being kept sufficiently 
moist by the evaporation of water, the conditions required for 
the formation of genuine patina are thus fulfilled. If the 
patina is to show a more bluish tone, brush the objects with a 
solution of 4^ ozs. of ammonium carbonate and 1 J ozs. of am- 
monium chloride in 1 quart of water, to which a small quan- 
tity of gum tragacanth may be added. 



524 ELECTRO-DEPOSITION OF METALS. 

A blue-green patina, much used in Paris, is produced by 
heating in the following solution : Water 500 grammes, cor- 
rosive sublimate 2.5 grammes, saltpetre 8.6 grammes, borax 
5.6 grammes, zinc oxide 11.3 grammes, copper nitrate 22 to 
22.5 grammes. 

A brown patina is obtained with the following solution : 
Oxalic acid 3 grammes, sal ammoniac 15 grammes, distilled 
water 280 grammes. 

'The article is to be frequently brushed with the solution ; 
this process requires considerable time. 

Patina for copper and brass. The production of two fine 
tones of color upon copper and brass articles is due to the fact 
that ammonia attacks and eventually dissolves copper. The 
following directions are given by La Nature : If to objects of 
copper is to be given the appearance of very antique art 
objects recently dug up, it is only necessary to immerse them 
in ammonia. The effect does not show itself immediately, 
but only after 24 hours. A beautiful dark green coating, 
which adheres quite firmly, is formed. By allowing the 
copper object to remain for several days in the fluid the sur- 
face is more strongly attacked and the antique effect is 
heightened. 

Another kind of patina which cannot be produced upon 
copper but only upon brass is obtained by immersing the 
object in a hot, nearly boiling, mixture of 75 cubic centimeters 
of ammonia, the same quantity of water and 10 grammes of 
potash. A uniform durable patina shows itself in half a 
minute. By allowing the article to remain. longer in the solu- 
tion the patina acquires, without being materially altered, a 
steely bluish-gray luster. 

To produce a steel-gray color upon copper, immerse the clean 
and pickled objects in a heated solution of chloride of anti- 
mony in hydrochloric acid. By using a strong electric cur- 
rent the objects may also be coated with a steel-gray deposit of 
arsenic in a heated arsenic bath. 

For coloring copper dark steel-gray, a pickle consisting of 1 



COLORING OP METALS. 525 

quart of hydrochloric acid, 0.125 quart of nitric acid, If ozs. 
of arsenious acid, and a like quantity of iron filings is recom- 
mended. 

Various colors upon massive copper. — First draw the object 
through a pickle composed of sulphuric acid 60 parts, hydro- 
chloric acid 24.5, and lampblack 15.5; or of nitric acid 100 
parts, hydrochloric acid If and lampblack J. Then dissolve 
in a quart of water, 4J ozs. of sodium hyposulphite, and in 
another quart of water, 14J drachms of blue vitriol, 5 J 
drachms of crystallized verdigris, and 7f grains of sodium 
arsenate. Mix equal volumes of the two solutions, but no 
more than is actually necessary for the work in hand, and 
heat to between 167° and 176° F. By dipping articles of 
copper, brass, or nickel in the hot solution they become im- 
mediately colored with the colors mentioned below, one color 
passing within a few seconds into the other, and for this 
reason the effect must be constantly controlled by frequently 
taking the objects from the bath. The colors successively 
formed are as follows : 

Upon copper : Upon brass : Upon nickel : 

Orange, Golden-yellow, Yellow, 

Terra-cotta, Lemon color, Blue, 

Red (pale), Orange, Iridescent. 

Blood-red, Terra-cotta, 

Iridescent. Olive-green. 

Some of these colors not being very durable, have to be 
protected by a coat of lacquer or paraffine. It is further 
necessary to diligently move the objects, so that all portions 
acquire the same color. The bath decomposes rapidly, and 
hence only sufficient for 2 or 3 hours' use should be mixed at 
one time. 

2. Coloring brass and bronzes. Most of the directions given 
for coloring copper are also available for brass and bronzes, 
especially those for the production of patinas and the oxidized 
tones by a mixture of ferric oxide and blacklead. 



526 ELECTRO-DEPOSITION OF METALS. 

Many colorations on brass are, however, effected only with 
difficulty, and are partially or entirely unsuccessful as, for 
instance, coloring black with liver of sulphur. As a pickle 
for the production of a 

Lustrous black on brass, the following solutions may be used : 
Dissolve freshly precipitated carbonate of copper, while still 
moist, in strong liquid ammonia, using sufficient of the cop- 
per salts so that a small excess remains undissolved, or, in 
other words, that the ammonia is saturated with copper. The 
carbonate of copper is prepared by mixing hot solutions of 
equal parts of blue vitriol and of soda, filtering off and wash- 
ing the precipitate. 

Dilute the solution of the copper salt in ammonia with one- 
fourth its volume of water, add 31 to 46 grains of graphite 
and heat to between 95° and 104° F. 

According to experiments in the laboratory of the Physikal- 
isch-Technischen Reichsanstalt, the following proportions have 
proved very effective : Copper carbonate 3| ozs., liquid am- 
monia 26| ozs., and an addition of 5| ozs. of water. Place 
the clean and pickled articles in this pickle until they show a 
full black tone, then rinse in water, immerse in hot water, 
and dry in sawdust. The solution soon spoils, and hence no 
more than required for immediate use should be prepared. 

For black pickling in the hot way, a solution of 21 ozs. of 
copper nitrate in 7 ozs. of water mixed with a solution of 3| 
grains of silver nitrate in ^ oz. of water, is recommended. 

Black of a beautiful luster may be produced, especially upon 
nickeled brass, by suspending the objects as anodes in a solu- 
tion of lead acetate (sugar of lead) in caustic soda, using a 
slight current-density. 

Black color on brass optical instruments is produced by plac- 
ing the brass in a solution of platinum or chloride of gold 
mixed with stannous nitrate. The Japanese bronze brass with 
a solution of copper sulphate, alum and verdigris. Success in 
bronzing depends on the temperature of the alloy, the propor- 
tions of metals used in the alloy, drying, and many other 



COLORING OF METALS. 527 

small details which can be learned only by practical experi- 
ence. 

Steel gray on brass. — Use a mixture of 1 lb. of strong hydro- 
chloric acid with 1 pint of water to which are added 5£ ozs. of 
iron filings and a like quantity of pulverized antimony sulphide. 

Hydrochloric acid compounded with white arsenic is also 
recommended for the purpose. The mixture is brought into 
a lead vessel, and the object dipped in it should be in contact 
with the lead of the vessel, or be wrapped around with a strip 
of lead. 

Solution of antimony chloride produces a gray color with a 
bluish tinge, and a hot solution of arsenious chloride in a 
small quantity of water a steel gray color. 

Silver color on brass. Dissolve in a well-glazed vessel 1^ 
ozs. cream of tartar and \ oz. of tartar emetic in 1 quart of 
hot water, and add to the solution If ozs. of hydrochloric 
acid, 4 J ozs. of granulated, or better, pulverized tin and 1 oz. 
of powdered antimony. Heat the mixture to boiling and im- 
merse the articles to be colored. After boiling at the utmost 
for half an hour, the articles will be provided with a beautiful, 
hard and durable coating. 

Pale gold color on brass. Dissolve in 90 parts by weight of 
water, 3.6 parts by weight of caustic soda, and the same 
quantity of milk sugar. Boil the solution \ hour. Then add 
a solution of 3.6 parts by weight in 10 parts by weight of hot 
water. Use the bath at a temperature of 176° F. 

Straw color, to brown, throvgh golden yellow, and tombac color 
on brass may be obtained with solution of carbonate of copper 
in caustic soda lye. Dissolve 5.25 ozs. of caustic soda in 1 
quart of water, and add If ozs. of carbonate of copper. By 
using the solution cold, a dark, golden-yellow is first formed, 
which finally passes through pale brown into dark brown with 
a green luster. Coloration is more rapidly effected by using 
the solution hot. 

Color resembling gold on brass, according to Dr. Kayser: 
Dissolve 8J drachms of sodium hyposulphite in 17 drachms 



528 ELECTRO-DEPOSITION OF METALS. 

of water, and add 5.64 drachms of solution of antimonious 
chloride (butter of antimony). Heat the mixture to boiling 
for some time, then filter off the red precipitate formed, and 
after washing it several times upon the filter with vinegar, 
suspend it in 2 or 3 quarts of hot water ; then heat and add 
concentrated soda lye until solution is complete. In this hot 
solution dip the clean and pickled brass objects, removing 
them frequently to see whether they have acquired the desired 
coloration. By remaining too long in the bath, the articles 
become gray. 

Brown color, called bronze Barbedierine, on brass. This beau- 
tiful color may be produced as follows : Dissolve b} 7 vigorous 
shaking in a bottle, freshly prepared arsenious sulphide in 
liquid ammonia, and compound the solution with antimonious 
sulphide (butter of antimony) until a slight permanent tur- 
bidity shows itself, and the fluid has acquired a deep yellow 
color. Heat the solution to 95° F., and suspend the brass 
objects in it. They become at first golden-yellow and then 
brown, but as they come from the bath with a dark dirty 
tone, they have to be several times scratch-brushed to bring 
out the color. If, after using it several times, the solution 
fails to work satisfactorily, add some antimonious sulphide. 
The solution decomposes rapidly, and should be prepared 
fresh every time it is to be used. 

A suitable solution may also be prepared by boiling 0.88 
oz. of arsenious acid and 1 oz. of potash in 1 pint of water 
until the acid is dissolved and, when cold, add 250 cubic 
centimeters of ammonium sulphide. According to the degree 
of dilution, brown to yellow tones are obtained. 

By this method only massive brass objects can be colored 
brown. To brassed zinc and iron, the solution imparts brown- 
black tones, which, however, are also quite beautiful. 

Upon massive brass, as well as upon brassed zinc, and iron 
objects, bronze Barbedienne may be produced as follows: Mix 
3 parts of red sulphide of antimony (stibium sulfuratum auran- 
tiannm) with 1 part of finely pulverized bloodstone, and tritu- 



COLORING OF METALS. 529 

rate the mixture with ammonium sulphide to a not too thickly- 
fluid pigment. Apply this pigment to the objects with a brush, 
and, after allowing to dry in a drying-chamber, remove the 
powder by brushing with a soft brush. 

In Paris bronze articles are colored dead-yellow or clay-yellow 
to dark brown by first brushing the pickled and thoroughly 
rinsed objects with dilute ammonium sulphide, and, after dry- 
ing, removing the coating of separated sulphur by brushing. 
Dilute solution of sulphide of arsenic in ammonium is then ap- 
plied, the result being a color resembling mosaic gold. The 
more frequently the arsenic solution is applied, the browner 
the color becomes. By substituting for the arsenic solution one 
of sulphide of antimony in ammonia or ammonium sulphide, 
colorations of a more reddish tone are obtained. 

Dead red color on brass. Suspend the articles, previously 
thoroughly freed from grease, in a solution of equal parts of 
potassium-lead oxide and red prussiate of potash heated to 
122° F. until they have acquired a sufficiently dark color. . 

For coloring brass articles in large quantities brown by boiling, 
the following solution is recommended : Water 1 quart, potas- 
sium chromate 1J ozs., nickel sulphate 1J ozs., potassium 
permanganate 4 J drachms. 

Solution of blue vitriol and potassium permanganate serves 
the same purpose. However, after, boiling, the articles must 
not be scratch-brushed, but after drying rubbed with vaseline. 

Violet and cornflower-blue upon brass: Dissolve in 1 quart of 
water 4^ ozs. of sodium hyposulphite, and in another quart of 
water 1 oz. 3| drachms of crystallized lead acetate (sugar of 
lead), and mix the solutions. Heat the mixture to 176° F., 
and then immerse the cleansed and pickled articles, moving 
them constantly. First a gold-yellow coloration appears, 
which, however, soon passes into violet and blue, and if the 
bath be allowed to act further, into green. The action is 
based upon the fact that in an excess of hyposulphite of soda, 
solution of hyposulphite of lead is formed, which decomposes 
slowly and separates sulphide of lead, which precipitates upon 
34 



530 ELECTRO-DEPOSITION OP METALS. 

the brass objects, and, according to the thickness of the 
deposit, produces the various lustrous colors. 

Upon the same action is based the spurious gilding of small 
silvered brass and tombac articles. Though this process has 
been known for many years, Joseph Dittrich obtained a Ger- 
man patent for it. He dissolves in 6J lbs. of water, 10| ozs. 
of sodium hyposulphite, and 3| ozs. of lead acetate (sugar of 
lead). 

Similar lustrous colors are obtained by dissolving 2.11 ozs. 
of pulverized tartar in 1 quart of water, and 1 oz. of chloride 
of tin in §■ pint of water, mixing the solution, heating, and 
pouring the clear mixture into a solution of 6.34 ozs. of sodium 
hyposulphite in 1 pint of water. Heat this mixture to 176° 
F., and immerse the pickled brass objects. 

Ebermayer's experiments in coloring brass. — Below the results 
of Ebermayer's experiments are given. In testing the direc- 
tions, the same results as those claimed by Ebermayer were 
not always obtained ; and variations are given in parentheses. 

I. Blue vitriol 8 parts by weight, crystallized ammonium 
chloride 2, water 100, give by boiling a greenish color. (The 
color is olive-green, and useful for many purposes. The color- 
ation, however, succeeds only upon massive brass, but not 
upon brassed zinc.) 

II. Potassium chlorate. 10 parts by weight, blue vitriol 10, 
water 1000, give b}^ boiling a brown-orange to cinnamon-brown 
color. (Only a yellow-orange color could be obtained.) 

III. By dissolving 8 parts by weight of blue vitriol in 1000 
of water, and adding 100 of caustic soda until a precipitate is 
formed, and boiling the objects in the solution, & gray- brown 
color is obtained, which can be made darker by the addition 
of colcothar. (Stains are readily formed. Brassed zinc ac- 
quires a pleasant pale-brown.) 

IV. With 50 parts by weight of caustic soda, 50 of sulphide 
of antimony, and 500 of water, a pale fig-brown color is pro- 
duced. (Fig-brown could not be obtained, the shade being 
rather dark olive-green.) 



COLORING OF METALS. 531 

V. By boiling 400 parts by weight of water, 25 of sulphide 
of antimony and 600 of calcined soda, and filtering the hot 
solution, mineral kermes is precipitated. By taking of this 5 
parts by weight and heating with 5 of tartar, 400 of water, 
and 10 of sodium hyposulphite, a beautiful steel-gray is ob- 
tained. (The result is tolerably sure and good.) 

VI. Water 400 parts by weight, potassium chlorate 20, 
nickel sulphide 10, give, after boiling for some time, a brown 
color, which, however, is not formed if the sheet has been 
pickled. (The brown color obtained is not very pronounced.) 

VII. Water 250 parts by weight, potassium chlorate 5, car- 
bonate of nickel 2, and sulphate of ammonium and nickel 5, 
give, after boiling for some time, a broivn-yellow color, playing 
into a magnificent red. (The results obtained were only in- 
different.) 

VIII. Water 250 parts by weight, potassium chlorate 5, 
and sulphate of nickel and ammonium 10, give a beautiful 
dark brown. Upon massive brass a good dark brown is ob- 
tained. The formula, however, is not available for brassed 
zinc. 

3. Coloring zinc. Direct coloring of zinc does not give, as a 
rule, reliable results, and it is therefore recommended to first 
copper or tin the zinc and color the coating thus obtained. 

Black on zinc. a. Dissolve crystallized copper nitrate 2 
parts and copper chloride 2 parts in acidulated water 64 parts, 
and add to the solution hydrochloric acid of 1.1 specific gravity 
8 parts. The resulting fluid has a slightly bluish color. A 
sheet of zinc, previously scoured bright by means of dilute 
hydrochloric acid and fine sand, will, when immersed in the 
fluid, immediately be colored intensely black. By removing 
the sheet thus treated, at once from the fluid and rinsing it 
without loss of time in a large quantity of pure water and 
allowing it to dry, the black coating will adhere very firmly 
to the zinc. 

b. Dip the object in a boiling solution of pure green vitriol 
5.64 ozs. and ammonium chloride 3.17 ozs. in 2§- quarts of 



532 ELECTRO-DEPOSTTION OF METALS. 

water. Remove the loose black precipitate deposited upon 
the object by brushing, again dip the object in the hot solu- 
tion and then hold it over a coal fire until the ammonium 
chloride evaporates. By repeating the operation three or four 
times, a firmly adhering black coating is formed. 

Gray, yellow, brown to black colors upon zinc. — Bring the 
articles into a bath which contains 6 to 8 quarts of water, 
3J ozs. of nickel-ammonium sulphate, 3J ozs. of blue vitriol 
and 3 \ ozs. of potassium chlorate. The bath is to be heated 
to 140° F. By increasing "the content of blue vitriol a dark 
color is obtained, and a brighter one with the use of a larger 
proportion of nickel salt. The correct proportions for the de- 
termined shades will soon be learned by practice. When 
colored, the articles are thoroughly rinsed, dried, without rub- 
bing, in warm sawdust, and finally rubbed with a flannel rag 
moistened with linseed oil, whereby they acquire deep luster, 
and the coating becomes more durable. 

Brown patina on zinc. — The objects are first coppered in a 
copper bath containing potassium cyanide, then in the acid- 
copper bath, rinsed, and finally suspended in a pickle consist- 
ing of a solution of 5.29 ozs. of blue vitriol and 2.82 ozs. of 
potassium chlorate in one quart of water at J 40° F., until they 
show the desired brown tone. They are then rinsed in water, 
scratch-brushed with a fine brass-brush, for a short time re- 
placed in the pickle, again thoroughly rinsed in water, and 
dried with a soft cloth. 

By suspending zinc in a nickel bath slightly acidulated with 
sulphuric acid, a firmly adhering blue-black coating is, after 
some time, formed without the use of a current. This coating- 
is useful for many purposes. A similar result is obtained by 
immersing the zinc objects in a solution of 2.11 ozs. of the 
double sulphate of nickel and ammonium and a like quantity 
of crystallized ammonium chloride in 1 quart of water. The 
articles become first dark yellow, then successively brown, 
purple-violet and indigo-blue, and stand slight scratch-brushing 
and polishing. 



COLORING OF METALS. 533 

A gray coating on zinc is obtained by a deposit of arsenic in 
a heated bath composed of 2.82 ozs. of arsenious acid, 8.46 
drachms of sodium pyrophosphate and If drachms of 98 per 
cent, potassium cyanide, and 1 quart of water. A strong cur- 
rent should be used so that a vigorous evolution of hydrogen 
is perceptible. Platinum sheets or carbon plates are used as 
anodes. 

A sort of bronzing on zinc is obtained by rubbing it with a 
paste of pipe-clay to which has been added a solution of 1 
part by weight of crystallized verdigris, 1 of tartar, and 2 of 
crystallized soda. 

Red-brown shades on zinc. Rub with solution of copper 
chloride in ammonia. 

Yellow-brown shades on zinc. Rub with solution of copper 
chloride in vinegar. 

4. Coloring iron. Browning of gun barrels. Apply a mix- 
ture of equal parts of butter of antimony and olive oil. Allow 
the mixture to act for 12 to 14 hours, then remove the excess 
with a woolen rag and repeat the application. When the 
second application has acted for 12 to 24 hours, the iron or 
steel will be coated with a bronze-colored layer of ferric oxide 
with antimony, which resists the action of the air, and may 
be made lustrous by brushing with a waxed brush. 

A patina which protects metals — iron, zinc, tin, etc. — from 
rust, is, according to Haswell, obtained as follows : The article, 
previously freed from grease and pickled, is suspended as 
negative electrode in a solution of 15J grains of ammonium 
molybdate and J oz. of ammonium nitrate in 1 quart of water. 
A weak current should be used — 0.2 to 0.3 ampere per 15J 
square inches. 

To protect gun barrels and other articles of iron and steel 
from rust, they are, according to Haswell, suspended as anodes 
in a bath consisting of a solution of lead nitrate and sodium 
nitrate, into which manganous oxide has been stirred. 

Lustrous black on iron. Apply solution of sulphur in tur- 
pentine prepared by boiling on the water-bath. After the 



534 ELECTRO-DEPOSITION OF METALS. 

evaporation of the turpentine a thin layer of sulphur remains 
upon the iron, which on heating immediately combines with 
the metal. 

A lustrous black is also obtained by freeing the iron articles 
from grease, pickling, and after drying, coating with sulphur 
balsam,* and burning in at a dark-red heat. If pickling is 
omitted, coating with sulphur balsam and burning-in must be 
twice or three times repeated. 

The same effect is produced by applying a mixture of three 
parts flowers of sulphur, and 1 part graphite with turpentine, 
and heating in the muffle. 

According to Meritens a bright black color can be obtained 
on iron by making it the anode in distilled water, kept at 158° 
F., and using an iron plate as cathode. The method was 
tested as follows : A piece of bright sheet pen-steel was placed 
in distilled water and made the anode by connecting it with the 
positive pole of a plating dynamo, and a similar sheet was con- 
nected with the negative pole to form the cathode. An electro- 
motive force of 8 volts was employed. After some time a dark 
stain was produced, but it lacked uniformity. The experi- 
ment was repeated with larger plates, when a good blue-black 
color was obtained on the anode in half a hour. On drying 
in sawdust the color appeared less dense, and inclined to a 
dark straw tint. The back of the plate was also colored, but 
not regularly. The face of the cathode was discolored with a 
grayish stain on the side opposite to the anode, but on the 
other side the appearance was almost identical with the black 
of the anode. The water became of a yellowish color. 

Fresh distilled water was then boiled for a long time so as 
to expel all trace of oxygen absorbed from the atmosphere, 
and the experiment repeated as in the former cases. No per- 
ceptible change took place after the connection had been made 
with the dynamo for a quarter of an hour. After the inter- 
val of one hour a slight darkening occurred, but the effect 

* Sulphur dissolved in linseed oil. 



COLORING OF METALS. 535 

was much less than that produced in five minutes in aerated 
water. 

The action of the liquid in coloring the steel is evidently one 
of oxidation, due to the dissolved oxygen, which becomes more 
chemically active under the influence of the electric condition, 
and gradually unites with the iron. 

The mat black coating upon clock cases of iron and steel — the 
so-called Swiss mat — is not produced by the electric process, 
but by a slow process of oxidation, ferroso-ferric oxide being 
formed. The objects, previously cleaned from grease with the 
greatest care, are brushed over by means of a sponge or brush 
with a ferric chloride solution, called ferroxydin, allowed to 
dry, and then steamed. For the production of a very strong 
mat, the process is to be twice or three times repeated. By 
one operation a beautiful black with semi-luster is obtained. 

Blue color on iron and steel. Immerse the article in | per 
cent, solution of red prussiate of potash mixed with an equal 
volume of |- per cent, solution of ferric chloride. 

Brown-black coating with bronze luster on iron. Heat the 
bright objects and brush them over with saturated potassium 
dichromate solution. When dry, heat them over a charcoal 
fire, and wash until the water running off shows no longer a 
yellow color. Repeat the operation twice or three times. A 
similar coating is obtained by heating the iron objects with a 
solution of 10 parts by weight of green vitriol and 1 part of 
sal ammoniac in water. 

To give iron a silvery appearance with high luster. — Scour the 
polished and pickled iron objects with a solution prepared as 
follows: Heat moderately 1J ozs. of chloride of antimony, 0.35 
ozs. of pulverized arsenious acid, 2.82 ozs. of elutriated blood- 
stone with 1 quart of 90 per cent, alcohol upon a water-bath 
for half an hour. Partial solution takes place. Dip into this 
fluid a tuft of cotton and go over the iron portions, using slight 
pressure. A thin film of arsenic and antimony is thereby de- 
posited, which is the more lustrous the more carefully the iron 
has previously been polished. 



536 ELECTRO-DEPOSITION OF METALS. 

5. Coloring of tin. — A bronze-like patina on tin may be ob- 
tained by brushing the object with a solution of If ozs. of blue 
vitriol and a like quantity of green vitriol in 1 quart of water, 
and moistening, when dry, with a solution of 3J ozs. of verdi- 
gris in 10J ozs. of vinegar. When dry, polish the object with 
a soft waxed brush and some ferric oxide. The coating thus 
obtained being not durable, must be protected by a coating 
of lacquer. 

Durable and very warm sepia-brown tone upon tin and its al- 
loys. — Brush the object over with a solution of 1 part of plat- 
inum chloride in 10 of water, allow the coating to dry, then 
rinse in water, and, after again drying, brush with a soft brush 
until the- desired brown luster appears. 

A dark coloration is also obtained with ferric chloride solu- 
tion. 

6. Coloring of Silver. — See " Deposition of Silver. " 
Electrochroma. The process for the production of colors on 

metals by electro-deposition, known under this term, is the 
invention of Mr. F. Arquimedas Rojaz. By this method either 
deposits or smuts of any desired color or texture can be pro- 
duced upon any metal used as a cathode. The anodes used 
are of pure carbon, no metal of any sort being put into the 
tank containing the plating solution except the work itself. In 
starting to color a piece of metal, be it brass, copper, tin, lead 
or iron, etc., the metal is first dipped into a cleaning solution, 
then into a hot water bath, next into the tank containing the 
solution for whatever background color is desired. A current 
of 8 to 12 volts pressure with a strength of 1 ampere per square 
inch of surface is used. After an immersion in the tank for 
from two to three minutes the work is dipped into hot water, 
and from there into a tub containing a dip solution. Here the 
finish of the process takes place, and the beautiful shades of 
color are produced. A piece of work, such as a lock plate for 
a store, may be given a green verde smut in the plating tank 
and then be changed to a light blue background in the dip tub- 
Gold finishes, rose antique and green, may be produced at 



COLORING OP METALS. 537 

will in a few seconds of time, without any gold in the solu- 
tion. 

All of the solutions used in the process are fully protected 
by patents and are furnished ready for use. They are said to 
be made up of more than half a dozen elements, the propor- 
tions of which are so evenly balanced that a slight variation 
in the amounts used of each ingredient will throw the entire 
solution out of gear. 



CHAPTER XV. 



LACQUERING. 



In the electro-plating industry recourse is frequently had to 
lacquering in order to make the deposits more resistant against 
atmospheric influences, or to protect artificially prepared colors, 
patinas, etc. Thin, colorless shellac solution, which does not 
affect the color of the deposit or of the patinizing, is, as a rule, 
employed/while in some cases colored lacquers are used to 
heighten the tone of the deposit, as, for instance, gold lacquer 
for brass. 

The lacquer is applied with a flat fine fitch brush, the ob- 
ject having previously been heated hand-warm. The brush 
should be frequently freed from an excess of lacquer, and the 
lacquer be applied as uniformly as possible without undue 
pressure of the brush. An excess of lacquer, which may have 
been applied, is removed by means of a dry brush. 

The lacquer for immediate use is kept in a small glass or 
porcelain pot, across the top of which a string may be stretched. 
This string is intended for removing by wiping the excess of 
lacquer taken up by the brush. Crusts of dried-in lacquer 
should be carefully removed, and the contents of the small pot 
should under no conditions be poured back into the can, as 
otherwise the entire supply might be spoiled. 

After lacquering, the object is dried in an oven at a temper- 
ature of between 140° and 158° F., small irregularities being 
thereby adjusted, and the layer of lacquer becoming trans- 
parent, clear and lustrous. 

Electro-plated articles which are to be lacquered must be 
thoroughly rinsed and dried to remove adhering plating solu- 
tion from the pores, otherwise ugly stains will form under the 
coat of lacquer. 

(538) 



LACQUERING. 539 

If it becomes necessary to thin a spirit lacquer, only absolute 
alcohol, i. e., alcohol free from water, should be used for the 
purpose, since alcohol containing water renders the coat of 
lacquer muddy and dull. 

The development in the art of lacquer-making has advanced 
with and in a measure kept pace with that made in the electro- 
deposition of metals. With the use of new metals, the intro- 
duction of new and altered formulas and processes for finishing 
metals, the employment of new and different chemicals, in fact 
with every change or alteration in the methods of finishing 
and using metals, changes have been made in the nature of 
the lacquers employed in their protection. 

Lacquers to be acceptable to the metal-worker must be per- 
fectly adapted to each special use, and not only suit the varied 
metals, finishes and conditions of the work, but also meet and 
overcome difficulties arising from, for instance, the influence of 
climatic changes and the use to which the lacquered metal is 
subjected. Many cases of trouble in the finishing of metal may 
now be traced to the use of an improper lacquer for the par- 
ticular metal or finish. Thus ingredients and chemicals which 
from their nature are antagonistic to a bronze metal and detri- 
mental to it should not be included in a lacquer for bronze, 
although the same ingredients may be beneficial to a silver, 
gold or aluminium surface. 

The most noted improvements have been effected in lacquers 
for brass bedsteads, gas and electric fixtures, black lacquers, 
and the lacquers made with the special object of saving time 
in their application and money in their use. 

A review of all the lacquers made for the above-mentioned 
purposes is not within the province of this work, and we must 
therefore confine ourselves to the enumeration of the newest 
and most important ones for general use, with which we have 
become familiar. 

Pyroxyline lacquers. — These lacquers, known under various 
names, such as Lastina, Pyramide and Obelisk, etc., were 
introduced to the trade in America as early as 1876, and were 



540 ELECTRO-DEPOSITION OF METALS. 

gradually adopted until early in the 80's, when their use be- 
came general, and since then they have become known 
throughout all parts of America and Europe. Pyroxyline 
lacquer represents a clear, almost colorless fluid, and smells 
something like fruit-ether, reminding one of bananas. It is 
chiefly used as a dip lacquer, though there is also a brush 
lacquer, which is applied with a brush, like spirit lacquer. 

The lacquer possesses the following good properties : The 
transparent, colorless coat obtained with it can be bent with the 
metallic sheet to which it has been applied without cracking. 
It is so hard that it can scarcely be scratched with the finger- 
nail, shows no trace of stickiness, and it is perfect]}' homogene- 
ous even on the edges. This favorable behavior is very likely 
due to the slow evaporation of the solvent, and the fact that the 
lacquer quickly forms a thickish, tenacious layer, which though 
moved with difficulty is not entirely immobile. Another ad- 
vantage of the lacquer — especially as regards the metallic 
objects — is that the coating in consequence of its physical 
constitution preserves the character of the bases. In accord- 
ance with the nature of pyroxyline, the coating is not sensibly 
affected by ordinary differences in temperature, and does not 
become dull and non-transparent, as is the case with resins, in 
consequence of the loss of molecular coherence. It can be 
washed w T ith water, and protects metals coated with it from 
the action of the atmosphere. It may also be colored, but of 
course only with coloring substances — mostly aniline colors — 
which are soluble in the solvent used. 

For lacquering articles by dipping, they should be as clean 
as for plating, and so arranged that the lacquer will run off 
properly. Allow them to drip over the drip tank until the 
lacquer stops flowing. Dry in a temperature of 100° to 120° 
F., if possible using a thermometer. Dip lacquers will dry in 
the air, but baking improves the finish. 

The receptacle for holding the lacquer and thinner for dip- 
ping purposes, should be either of glass, stoneware, chemically 
enameled iron, or a tin-lined wooden box — the preference be- 



LACQUERING. 541 

ing in the order named. Lacquer or thinner should never be 
placed in copper or galvanized iron tanks. 

For thinning the lacquer when it has become too thick by 
the evaporation of the solvent, use the thinner which is recom- 
mended for each particular grade of lacquer. 

The appearance of rainbow colors upon objects lacquered 
with pyroxyline lacquer is due either to insufficient cleanli- 
ness, especially to the presence of grease upon the objects, or 
to the lacquer having been too much diluted. Objects to be 
lacquered should be freed from grease by the use of platers' 
compound, rinsed in hot water, dried in thinner and then 
lacquered. The use of benzine, aside from the danger it en- 
tails, is not always effective in removing grease from the pores 
of the metal. After cleaning, the polished surface of the work 
should not be touched with the hands. If the rainbow colors 
are due to the lacquer having been too much thinned, let the 
vessel containing it stand uncovered for some time in a place 
free from dust, so that it becomes somewhat more concentrated 
by the evaporation of the solvent, or correct the tendency to 
rainbow colors by adding more undiluted lacquer to the mix- 
ture. In adding thinner to lacquer it is always advisable to 
give it plenty of time to act upon the pigment in the lacquer. 
This can be facilitated by stirring with a wooden paddle. 

Very nice shades of color can be produced by coating the 
objects, previously well cleansed from grease, with lacquer by 
dipping, allowing the coat to become dry, then suspending the 
objects for a few seconds in golden-yellow, red, green, etc., 
d}^es, known as dipping colors, next washing in water and 
finally drying. By mixing the coloring dyes in various pro- 
portions nearly every desired tone of color can be obtained. 

Special invisible lacquer for ornamental cast and chased interior 
grille, rail and enclosure ivork. This lacquer is made in three 
grades for use, 1, with the brush ; 2, with the spraying 
machine ; and 3, as a dip lacquer. Its presence cannot be 
detected on any of these sensitive finishes, and the fine mat 
finishes are left without the slightest luster after it has been 



542 ELECTRO-DEPOSITION OF METALS. 

applied thereto. It can be mixed with the pigment fillings 
so much used in cast ornamental mountings, figured mould- 
ing for the verds, Florentine, rose and antique effects. Sand- 
blasted and brushed plain parts will not take on a sheen from 
this lacquer and will, therefore, not make a contrast in the 
lights of the filled and smooth portions of the work. The 
fine reliefs in these finishes, it has been found, will not be 
disturbed because of the lacquer softening the pigments when 
it is applied by spraying. In use this lacquer can be thinned 
so as to flow away from the various parts that make up a 
grille or rail without leaving any lines or waves, or causing 
glossy places or variations of lines. This lacquer is made by 
The Egyptian Lacquer Manufacturing Co., of New York, and 
with it the rich subdued effects of dead, mat, sanded and 
semi-dead finishes can be protected without in the least 
affecting their appearance. 

Satin finish lacquer is made by the same concern just men- 
tioned ; it comes in two grades, one for brush and the other 
for dip work. Its purpose is to maintain the light, but some- 
what solid, effect in which body color rather than tints pre- 
dominate ; its deadness gives to these body effects a plastic 
appearance. It can be used to protect a velvet-like tint re- 
sembling the ground gold, frosting or satin finish seen in 
ormolu and colonial gold, as well as dead and dull surfaces, 
or unpolished, lusterless and mat gold and mat silver. It can 
also be used to create a dead luster, or a deadened lustrous 
surface, for example, on mat designs upon a lustrous ground, 
where the lacquer lights up the satin finish. Jewelry, silver 
and novelty manufacturers can use it for general finishing of 
their work, as it will not alter the sensitive metal colorings, 
nor will it fill up to a gloss delicately brushed, satined, or 
chased surfaces or smut tints. 

Dip lacquer for pickled castings to be copper-plated and oxi- 
dized. Articles made from iron and steel castings that are 
pickled or water rolled, or from hot-rolled steel, where the 
scale is pickled off, or any other similar work which is pre- 



LACQUERING. 543 

pared by the same inexpensive method, when copper-plated 
and oxidized, must be lacquered with a lacquer which will 
give life to the naturally dead surface of the metal and to the 
smut left from the oxidation when not scratch-brushed. This 
is a very rapid and inexpensive process since it does away 
with the costly operations of polishing, scratch-brushing and 
cleaning ; the finish depends entirely upon the life and luster 
of the lacquer, hence it is best to use one of the lacquers now 
designated. 

With helios dip lacquer, special, which is made by The 
Egyptian Lacquer Manufacturing Co., of New York, a fine 
luster is given to the dead backgrounds and a bright and 
lustrous finish to the smooth parts of the work and in many 
respects this lacquer renders the work equal to that which has 
been polished. Many other lacquers which have been tried 
dry down to the natural deadness of the metal finish and 
consequently the effect of the plating and oxidizing is lost, or, 
if not entirely lost, is not brought out in its right color. 

Old brass or brush-brass finishes. From 90 to 95 per cent of 
all brass for gas and electric fixtures, bedsteads and similar 
work is finished in brush-brass. Lacquers are specially made 
for the high gloss effects, as well as for the dull, or antique 
finish. As this finish is more susceptible to tarnish and stain 
than any other known finish, it is important that precise 
particulars be given as to the handling of this work prelim- 
inary to lacquering. For instance, where this work is finished 
with pumice, sand, flint, etc., and water, as most of it is, it 
should, as fast as completed be placed in a tank containing 
borax solution made by dissolving 1 lb. powdered borax in 
hot water and adding enough water to make 5 gallons. Use 
cold. Let the work accumulate in the solution until ready 
to lacquer. Then rinse the work in hot water and dip it in 
thinner. It will dry without stain by hanging up for a 
moment or two, when it should be immediately lacquered. 

Where " old brass composition " or emery and oil is used, 
the work should be cleaned from grease in " plater's com- 



544 ELECTRO-DEPOSITION OF METALS. 

pound " or some other non-tarnishing cleaner, and can be 
placed in the borax -solution as fast as finished on the brush. 
It is then rinsed in hot (not too hot) water, dried in thinner, 
and immediately lacquered. 

Wiping the surface with a soft cloth or chamois skin does 
not remove the moisture from the metal. This is particularly 
apparent when there is much humidity in the air, and ver- 
digris or oxide rapidly forms in the scratches made by the 
abrasive materials and causes much subsequent trouble. The 
heat of the oven converts this moisture, combined with the 
oxide, into steam which penetrates the lacquer and causes 
staining of the film. Sawdust should never be used for 
drying metals given an old-brass finish. 

Brush brass finish lacquers. This very sensitive and easily 
discolored finish is readily marred by the use of an inefficient 
transparent dip lacquer. No existing finish requires more 
exacting and careful treatment than the brush brass finish, 
the finely brushed lines attracting and retaining substances 
which tarnish it readity. As a rule these substances are not 
visible, and cannot be easily removed by ordinary cleaning 
methods. After a time every speck of dirt shows under the 
lacquer coating, and is the cause of the various discolorations 
often seen in brush brass finish ; they vary from the tints 
shading into the browns to tints running into the greens, and 
are in almost every instance caused by the oxidizing influ- 
ences of contaminating matters left upon or attracted by the 
metal before it has been lacquered. When work is handled 
in large quantities these imperfections are especially notice- 
able, for such work cannot always be inspected one piece at a 
time. The old method of drying the buffed and smooth-sur- 
faced finishes with sawdust and then rubbing them with a soft 
muslin material is inadequate as well as uncertain for the 
brush brass ; in fact this process primarily causes the imper- 
fections which it is intended to prevent. At any rate, the 
result is necessarily doubtful when brush brass is dried in this 
way and allowed to stand for even a very short time before it 
is protected with lacquer. 



LACQUERING. 545 

Egyptian brush brass dip lacquer and brush brass thinner, 
made by the Egyptian Lacquer Manufacturing Co., of New 
York, meets the necessary and varied conditions called for by 
this finish. After the brush brass has been washed in plater's 
compound and well rinsed in cold and hot waters, the work 
is first dipped into the brush brass thinner, which absorbs all 
moisture left on the metal and removes whatever impurities 
may have been attracted to it, and prepares the work for its 
dip into the brush brass dip lacquer. By the dip into the 
thinner a chemically pure metal surface is provided for the 
reception of the lacquer coating, and this guarantees the brush 
brass finish itself against discoloration, since 'the lacquer has 
been applied to a practically chemically clean and pure 
surface. 

Brush brass work which cannot be conveniently dip- 
lacquered should be spray-lacquered in preference to lacquer- 
ing with a brush, because the fine irregularities of the brushed 
surface of the metal retard the free flow of a brush lacquer. 
In other words, a brush lacquer cannot be applied quite as 
effectively as on a smooth finish, for, owing to the irregu- 
larities of the metal surface spoken of, an obstruction is placed 
in the way of the flowing of the lacquer when it is applied 
with a brush, because with the use of the latter the separa- 
tions in the lacquer, due to the uneven distribution of it from 
the bristles of the brush, sometimes leave minute parts of the 
surface unlacquered and the irregularities of the brushed 
metal surface prevent the lacquer from spreading over these 
minutely exposed lines. Thus when applying the lacquer 
with a brush it happens now and then that the exposed and 
unlacquered portions tarnish and destroy the appearance of 
the entire work. On large articles the lacquer should be 
sprayed, and the article itself turned by mechanical means 
during the application of the lacquer, so as to give momentum 
to its flow, thereby insuring its even distribution. 

Brass bedstead lacquering. Complaints of the same kind, 
namely, streaks in lacquered work, have been the cause for 
35 



546 ELECTRO-DEPOSITION OF METALS. 

replacing brush lacquering of brass bedsteads by the spray. 
Since the vogue for satin and drawn emery finishes have taken 
the place of the old English gilt bedstead finish the spraying 
process has become even more necessary. The unusual depth 
of the cut in the metal surface made by these finishes has cre- 
ated a new problem for lacquer makers. The lacquer used on 
this work should be unusually heavy, in fact heavy enough 
and dense enough to fill these abnormally penetrated surfaces, 
for the lacquer film must in all instances be built up so as to 
protect the highest exposed points of this finish. The lacquer 
for this finish must be applied with a spray since it is neces- 
sary that a thick and plastic coating should be applied, one 
indeedwhich when dry shall be hard and tough enough to 
resist marring from the usual rough and severe treatment to 
which a bedstead is subjected. 

Dead black lacquers produce imitation dead and mat finishes. 
These are variously known as imitation Bower Barff, wrought 
iron, ebony or rubber finishes. If the same preliminary steps 
are taken in preparing metal goods for the black lacquers as 
for japan and enamel, just as durable and lasting results will 
be obtained in a small fraction of the time and at a minimum 
cost in labor. The best class of japanning on iron castings, 
hot or cold rolled steel requires two coats of either thin japan 
or some other similar preparation, each coat requiring several 
hours' baking, and usually a delay of several days before the 
surface of the last coat is in condition to be rubbed down. 

To get the same results with the black lacquers on sand 
pitted cast iron, two coats of metallic filler, applied with a brush, 
baked a short time at about 180° F. to harden, and then 
rubbed down with fine emery cloth or No. 2 garnet paper, fol- 
lowed by one or two air-drying coats of lacquer will be suffi- 
cient. On smooth-surfaced metals one or two thin coats of 
lacquer can be applied in place of the metallic filler as a base 
for the final coat. In many cases one coat of the lacquer will 
be found sufficient to give the desired finish, and the entire 
process may be completed in a few hours, where it will re- 



LACQUERING. 547 

quire from one to five days to secure the same finish with 
japan, and besides all the equipment necessary for the latter 
will be entirely eliminated. 

If desired, the metal can be given a light copper plate and 
then be oxidized as a base for the finishing coat of black 
lacquer. 

For high luster finishes such as are obtained with enamels, 
glossy, black lacquers are used, and to increase the brilliancy 
and high luster the same as with enameled goods which are 
given a finishing coat of baking varnish, a high grade of 
transparent lacquer is used over the glossy black lacquer the 
same as the varnish on the enamel. 

On goods made from non-ferrous metals such as high-grade 
optical goods, opera and field glasses, and all classes of instru- 
ment work, where sliding tubes and other parts are to be 
finished with a glossy or dead black lacquer, where both 
beauty and great durability are the chief essentials, the surface 
of the brass should be first prepared by chemically blacking 
the metal with copper-ammonia or any other good black dip. 
Then a filling coat of any black lacquer, preferably a dead 
black, should be used. The surface is then in perfect condition 
for the finishing coat of black lacquer. A black background 
and very adhesive surface are obtained by this method, and the 
finish will withstand the hard usage these goods are made for. 

Dead black lacquer as a substitute for Bower-Barff. The 
genuine Bower-Barff is a matted black finish for iron and 
steel. It is produced by heat and steam liberating the oxygen 
from the iron and forming magnetic oxide. 

The oven and other equipment required for this finish is 
not practicable in the average factory, as the demand for 
goods in this finish, outside builders' hardware, is not com- 
mensurate with the cost of providing and maintaining a plant 
for this purpose. 

A number of imitation finishes are made, by using solutions 
of sulphur and linseed oil, sulphur, graphite and turpentine, 
and other similar solutions. A coating of these mixtures is 



548 ELECTRO-DEPOSITION OF METALS. 

applied and the metal heated to a red heat to burn it in or 
else the goods are baked in a muffle. But they are all slow 
and uncertain processes, and some kind of special equipment 
must be provided to do this work. 

The method for obtaining this finish most in use, and for 
which any plating-room is equipped, is by using an antique 
black or Bower-Barff lacquer. Such lacquer has a number of 
advantages over the above-described processes, which can 
only be used on iron or steel ; the lacquer will give the finish 
on any metal. 

To get the Bower-Barff on iron or steel the metal should 
first be lightly copper-plated and oxidized ; and if brass or 
bronze is used it is only necessary to oxidize the metal with 
any black dip, or electro-oxidize. Then the antique black 
lacquer is applied for the finish. The lacquer can also be 
lightly sand-blasted if an increased mat is desired. 

In the above-described processes good results are obtained 
by the use of the following lacquers, made by the Egyptian 
Lacquer Manufacturing Co. of New York : Dead Blacks, Egyp- 
tian Antique Blacks, Ebony, and Rubber Finish Lacquers. 

Spraying of lacquers. — The application of lacquers by the 
pneumatic air spray having for the last few years been gradu- 
ally adopted,- has proved advantageous in finishing various 
goods, the success in application depending upon many minor 
details of manipulation ; these come readily to the lacquerer 
while using the spray. 

The spraying machine consists of a pump, called a com- 
pressor, generating the air, transferring the air to a storage 
tank. If this pump is automatic, copper flexible tubing is 
used, if stationary, a gas pipe. The storage tank which holds 
the air, has a gauge indicating the number of pounds carried. 
A safety valve is also on the tank to control the air. These 
tanks vary a great deal ; it depends entirely upon the number 
of cups drawing off the air and the air must be regulated ac- 
cordingly. It will run from 18 lbs., and in some cases as 
high as 60. There is a rubber hose of flexible copper tube 



LACQUERING. 549 

connected to the storage tank long enough to cover the entire 
work -bench to which the cups are fastened. The cup or con- 
tainer is an atomizer throwing a spray very much the same as 
a perfume atomizer, although it is made in sizes from half a 
pint to a quart. Cups or containers are made both of glass 
and metal. Some prefer the glass for the reason that it is 
possible to see the lacquer in the container at any time. Glass 
cups have, however, the drawback of liability of breakage 
which may result from careless or rough usage about the shop, 
and besides some sprays are so constructed that under certain 
conditions it is an easy matter for the air pressure to be acci- 
dentally switched directly into the container, and with a pres- 
sure of 40 lbs. both container and lacquer are destroyed. For 
these reasons it would seem that metal containers are to be 
preferred. The spray ma}^ be gauged by a small catch on the 
side of the nozzle. This style of sprayer is considered very 
practical, although there are many more complicated ones in 
the market. 

The equipment to be used in producing the air, storing it 
and in forcing it to the spray in a pure condition should be 
of sufficient capacity and be provided with the proper appli- 
ances to guard against fluctuations which in the flow of the 
lacquer stream itself interferes with the continuous flow of the 
lacquer. This flow of necessity must be uniform in strength 
and outflow, else the results cannot fail to be irregular. It 
naturally follows that the compressor which regulates this 
must be such as to be capable of sustaining this pressure 
uninterruptedly. The quality of the lacquering changes with 
the irregularity of the pressure. The air should be taken 
from a part of the building which is far removed from the 
steam exhausts or other localities where the air or atmosphere 
is impure or moist ; the drier the air, the less condensed water 
will enter into the pipe line. The air should be stored in a 
tank close to where the spray is in use, for this helps in the 
precipitating of impurities just before it goes into the lacquer, 
and the extra volume close at hand steadies the pressure. A 



550 ELECTRO-DEPOSITION OF METALS. 

reducing valve in the line between the tank and spray, which 
can be drained occasionally, is another precaution which may 
be provided against the admission of water. The addition of 
a filter will be found to be of great advantage, as it will catch 
the most minute particles of oil, moisture and dirt just before 
the air reaches the flexible hose to which the spray is attached. 

Assuming that both the pressure and clean air referred to 
can be relied upon, then the next thing necessary is to use 
the lacquer in as heavy a condition as possible. By this is 
meant that it should be neither too heavy nor too light for 
the air to raise it to the nozzle, atomize it and apply it by 
flowing it out from the spray upon the work in an even and 
heavy film. 

The lacquer should never be thinned so as to make it easier 
in the spray, for in that case the lacquer will create runs upon 
the surface of the work; if unusual thinning is necessary to 
get an even flow from the spray then either the pressure or 
the adjustment of the spray, or the spray itselt, is at fault. 
While the lacquer is being applied from the spray the work 
which is being lacquered should be kept moving in a revolv- 
ing motion in order to insure an even distribution of the lac- 
quer, and avoid an uneven distribution of it ; in other words, 
to prevent matting. 

The high pressure used drives the lacquer onto the object, 
after which, however, the liquid must take care of itself, and 
it must then flow together into a smooth surface, or else the 
whole process is worthless. 

The spraying-on of lacquers to be successfully used depends 
not only upon the nature of the articles sprayed, but upon the 
lacquer itself. Special lacquers have been made for these pur- 
poses, and with them success may readily be obtained. A 
special lacquer has been made for lamps, chandeliers and gas 
fixtures ; another for silver and white metals ; another for 
builders' hardware. With these when applied uniformly, the 
lacquer spreads evenly and covers the surface entirely with- 
out break, and presents an unusually uniform appearance with- 



LACQUERING. 551 

out disfiguring blotches or patches, indicating an unequal thick- 
ness of lacquer. 

Most of the lacquers which we have seen tested were made by 
The Egyptian Lacquer Manufacturing Company of New York. 
In many instances it will be found that ordinary operators 
with less skill than the trained lacquerer can do very satisfac- 
tory work with these machines. 

Spraying black lacquers. By applying the black lacquers 
with a spra}' various finishes heretofore made with either 
baking enamels or japans can now be finished with black 
lacquer. Whenever great durability and toughness are essen- 
tial and where the fine finish made with the black lacquer is 
but a secondary consideration, a priming lacquer should be 
first applied to the work ; after this the black lacquer should 
be sprayed over it. Such a finish makes up in toughness and 
tenacity the slight runs in its appearance. A second coating 
of black lacquer without this priming coat will not be proof 
against the hard usage to which some of these finishes are 
frequently exposed. 

A coat of priming lacquer is of great advantage in many 
instances where the metal surface is not of an adhesively 
magnetic nature, or on a metal that cannot be entirely pre- 
vented from taking an oxide if exposed to the air even only 
during the short time of lacquering. The coat of priming 
lacquer is also a desirable preventative where large quan- 
tities of work are being lacquered and where cleanliness of 
the work cannot always be absolutely relied upon. Peeling 
and chipping, either or both, are often caused by the inex- 
perience of the lacquerer in mixing the lacquer ; if the body 
is thinned to the extent that it weakens the binding qualities 
of the material something of the kind is bound to happen. 

Since the advent of antique effects, such as mission and 
Flemish, and other dark and subdued finishes on furniture, 
etc., the manufacturers of art metal goods have given close 
attention to having their goods in conformity with the furni- 
ture and trimmings in buildings. 



552 ELECTRO-DEPOSITION OF METALS. 

They have found the dead black lacquers the best for this 
purpose, and the question of application has been solved by 
the spray, as it was impossible to get the fine results they re- 
quire by either brushing or dipping the black lacquers, for 
unless the operator was skilled in the application of lacquers 
by these methods there would be such imperfections as streaks, 
laps, runs or drip. With the spray all these difficulties are 
obviated and the finish cannot be otherwise than perfect, and 
the lacquer thereby used to the best advantage, with the fine 
result intended for it by the makers. 

To use the spray successfully for this purpose, the base used 
in the lacquer must be adapted to go through the spray 
nozzle without clogging and going onto a surface lumpy. 
With the spray any of the blacks proposed by The Egyptian 
Lacquer Manufacturing Co. can be applied on all classes of 
metals, whether of a design with deep indentations or inter- 
stices or on the flattest surface, with artistic perfection. 

The same can be said about the finishing of other goods, 
such as slate electric switchboards, gas stoves, heaters, steel or 
other box enclosures, cast parts, steel or brass stampings, or, in 
fact, all other articles made from any of the metals or any of 
the alloys. 

The black lacquers will retain their original finish and re- 
main black under heat. And there is no other black made 
that will adorn this class of goods the same from the points of 
beauty, durability and salableness. Stoves and heaters have 
large and porous surfaces as the sheet metal is left in its 
natural condition just as it comes from the rolling mill, and 
for this reason it has been found difficult to apply the black 
lacquer with a brush, but the spray puts it on perfectly, and 
transforms it from an object of roughness to one of uni- 
formity. To avoid marring the nickel trimmings during the 
operation of spraying, a mask or other covering is used to 
protect those parts, and it is then a very rapid process. 

This also applies to all other articles constructed from the 
same material and on the same order of the stoves and heaters. 



LACQUERING. 553 

On other metal goods, where designs or ornaments are to be 
put on, with black or other colored lacquers, stencils are used, 
and the lacquers sprayed onto it. With the spray application 
there will be no runs or other disfigurement of the design. 

The spray, with the blacks or other colored lacquers, can 
be used. 

Water-dip lacquers and their use. — These lacquers are not, as 
often believed, lacquers in which water is used. Their name 
is derived from the fact that after the metal has been dipped 
or plated, it may, while wet and without drying it, be dipped 
into the lacquer without in any way affecting the metal finish. 

The advantage of water-dip lacquers is readily appreciated 
by the manufacturers who are rapidly adopting them for many 
classes of small work. They are especially well adapted for 
bright-dipped finishes, such as are usually finished in bulk by 
basket dipping. Tarnish affects this finish almost instantly 
if it is allowed to dry and then lacquered in the usual way ; 
therefore the lacquering must be carried out as soon as the 
dipping process has been finished. 

The most flagrant example of tarnishing is in the case of 
plated work, particularly goods copper-plated, and to prevent 
tarnishing, such goods must be lacquered at once. Even the 
customary drying-out will usually not suffice to prevent the 
tarnishing, and the result is either the increase in labor in 
handling the goods, or the production of a large amount of 
imperfect goods. 

The method of drying work in sawdust before lacquering, 
with the consequent carrying of sawdust into the lacquer, and 
the frequent discoloration of the finish by wet sawdust, can be 
entirely eliminated, and this one important improvement 
alone in handling such work has brought about an extensive 
use for the water-dip lacquers. 

Since the advent of mechanical platers water-dip lacquers 
have another and new field, as the goods plated in this way 
can be put into a mesh basket as soon as taken from the plater 
and lacquered, which not only gives the finish immediate pro- 



554 ELECTRO -DEPOSITION OF METALS. 

tection but is in keeping with the quickness and low cost of 
this method. 

Points to follow when using water-dip lacquers for small work, 
such as cupboard catches, window fasteners, cheap building 
and trunk hardware, coat hooks, tacks, furniture nails, and 
other small specialties and novelties. The work may be placed 
in a wire mesh basket, rinsed in. cold and hot water, dipped 
into the lacquer, which can be used so thin that there will be 
no accumulation or drip left, and the work can be dried in 
bulk without the pieces sticking together. The goods thus 
lacquered can be put right into a box and sent to the shipping 
room where they will dry out hard and with a high luster. 

The water-dip lacquers, made by The Egyptian Lacquer 
Manufacturing Company of New York, contain ingredients 
which permit lacquering in bulk of small brass-plated work? 
copper acid-dipped or oxidized finishes being rinsed in either 
hot or cold water, and without drying dipped directly into the 
lacquer. Electro-deposited copper oxidizes rapidly, and espe- 
cially so in a humid atmosphere. An instant application of 
these lacquers, while the work still retains its luster is recom- 
mended. It is very desirable for bulk, basket or en-masse 
lacquering. 

A large collection of small articles can be perfectly lacquered 
by simple immersion. 

Syphon out the water every morning from the lacquering 
tank, either with a rubber hose or by means of a faucet at the 
bottom of the tank. 

A wire screen, nickel-plated and with a coarse mesh, should 
be placed in the lacquer jar or tank, three or four inches from 
the bottom. This will prevent the work from being dipped 
through the lacquer into the precipitated water, which lies at 
the bottom of the jar. All dirt and foreign matter carried into 
the lacquer with the work will sift through the screen and can 
be drawn off with the water. 



CHAPTER XVI. 

HYGIENIC RULES FOR THE WORKSHOP. 

In but few other branches of industry has the workman so 
constantly to deal with powerful poisons as well as other sub- 
stances and vapors, which are exceedingly corrosive in their 
action upon the skin and the mucous membranes, as in electro- 
plating. However, with ordinary care and sobriety, all influ- 
ences injurious to health may be readily overcome. 

The necessity of frequently renewing the air in the workshop 
by thorough ventilation has already been referred to in chapter 
IV, " Electro-plating Establishments in General." Workmen 
exclusively engaged in pickling objects are advised to neutral- 
ize the action of the acid upon the enamel of the teeth and the 
mucous membrane of the mouth and throat by frequently 
rinsing the mouth with dilute solution of bicarbonate of soda. 
Those engaged in freeing the objects from grease lose, for want 
of cleanliness, the skin on the portions of the fingers which 
come constantly in contact with the lime and caustic lyes. 
This may be overcome by frequently washing the hands in 
clean water; and previous to each intermission in the work the 
workman should, after washing the hands, dip them in dilute 
sulphuric acid, dry them, and thoroughly rub them with cos- 
moline, or a mixture of equal parts of glycerine and water. 
The use of rubber gloves by workmen engaged in freeing the 
objects from grease cannot be recommended, they being ex- 
pensive and subject to rapid destruction. It is better to wrap 
a linen rag seven or eight times around a sore finger, many 
workmen using this precaution to protect the skin from the 
corrosive action of the lye. 

It should be a rule for every employee in the establishment 
not to drink from vessels used in electro-plating manipula- 

(555) 



556 ELECTRO-DEPOSITION OF METALS. 

tions ; for instance, porcelain dishes, beer glasses, etc. One 
workman may this moment use such a vessel to drink from, 
and without his knowledge another may employ it the next 
morning for dipping out potassium cyanide solution, and the 
first using it again as a drinking vessel may incur sickness, or 
even fatal poisoning. 

The handling of potassium cyanide and its solutions re- 
quires constant care and judgment. Working with sore hands 
in such solutions should be avoided as much as possible ; but 
if it has to be done, and the workman feels a sharp pain in 
the sore, wash the latter quickly with clean water, and apply 
a few dxops of blue vitriol solution. 

Many individuals are very sensitive to nickel solutions, 
eruptions which are painful and heal slowly breaking out 
upon the arms and hands, while others may for years come in 
contact with nickel baths without being subject to such erup- 
tions. In such cases prophylaxis is also the safeguard, i. e., 
to prevent by immediate thorough washing the formation of 
the eruption if the skin has been brought in contact with the 
nickel solution, as, for instance, in taking out with the hand 
an object which has dropped into a nickel bath. 

Poisoning by prussic acid, potassium cyanide and cyanide com- 
binations. — In cases of internal poisoning first aid must be 
quickly rendered and a physician immediately called. There 
is but little hope of saving the life of a person poisoned by 
prussic acid, as well as when potassium cyanide or soluble 
cyanide combinations in large quantities have been taken into 
the stomach. In such cases solution of acetate of iron should 
be quickly administered and the patient made to inhale some 
chlorine prepared by putting a teaspoonful of chloride of lime 
in water acidulated with a small quantity of sulphuric acid. 
Water as cold as possible should at intervals be also poured 
over the head of the patient. 

Poisoning by copper salts. — The stomach should be quickly 
emptied by means of an emetic or, in want of this, the patient 
should thrust his finger to the back of his throat and induce 



HYGIENIC RULES FOR THE WORKSHOP. 557 

vomiting by tickling the uvula. After vomiting, drink milk, 
white of egg, gum-water, or some mucilaginous decoction. 

Poisoning by lead salts requires the same treatment as poison- 
ing by copper-salts. A lemonade of sulphuric acid, or an alka- 
line solution containing carbonic acid, such as Vichy water or 
bicarbonate of soda, is also very serviceable. 

Poisoning by arsenic. — The stomach must be quickly emptied 
by an energetic emetic, when freshly precipitated ferric hydrate 
and calcined magnesia may be given as an antidote. Calcined 
magnesia being generally on hand, mix it with 15 or 20 
times the quantity of water, and give of this mixture 5 or 6 
tablespoonfuls, every 10 to 15 minutes. 

Poisoning by alkalies. — Use weak acids, such as vinegar, 
lemon juice, etc., and in their absence sulphuric, hydrochloric 
or nitric acid diluted to the strength of lemonade. After the 
pain in the stomach has diminished, it will be well to adminis- 
ter a few spoonfuls of olive oil. 

Poisoning by mercury salts. — Mercury salts, and particularly 
the chloride (corrosive sublimate), form with the white of egg 
(albumen) a compound very insoluble and inert. The remedy, 
albumen, is therefore indicated. Sulphur and sulphuretted 
water are also serviceable for the purpose. 

Poisoning by sulpliuretted hydrogen. — The patient should be 
made to inhale the vapor of chlorine from chlorine water, 
Javelle water, or bleaching-powder. Energetic friction, espe- 
cially at the extremities of the limbs, should be employed. 
Large quantities of warm and emollient drinks should be given, 
and abundance of fresh air. 

Poisoning by chlorine, sulphurous acid, nitrous and hyponitric 
gases. — Admit immediately an abundance of fresh air, and ad- 
minister light inspirations of ammonia. Give plenty of hot 
drinks and excite friction in order to conserve the warmth and 
transpiration of the skin. Employ hot foot-baths to remove 
the blood from the lungs. Afterwards maintain in the mouth 
of the patient some substance which, melting slowly, will keep 
the throat moist, such as jujube and marshmallow paste, mo- 
lasses candy, and licorice paste. Milk is excellent. 



CHAPTER XVII. 

GALVANOPLASTY (REPRODUCTION). 

By galvanoplasty proper is understood the production, with 
the assistance of the electric current, of copies of articles of 
various kinds, true to nature, and of sufficient thickness to 
form a resisting body, which may be detached from the object 
serving -as a mould. 

By means of galvanoplasty we are enabled to produce a 
simple, smooth plate of copper of such homogeneity as never 
shown by rolled copper, and such copper plates are used for 
engraving. From a medal, copper-engraving, type or other 
metallic object, a galvanoplastic copy may be made, which is 
to be considered as the negative of the original, in so far as it 
shows the raised portions of the original depressed, and the 
depressed portions raised. If now from this negative a fresh 
impression be made by galvanoplasty, the result will be a true 
copy of the original, possessing the same sharpness and fine- 
ness of the contours, lines and hatching. 

A true reproduction of plastic works of art can in the same 
manner be made, but a current-conducting surface is required 
for effecting the deposit. As seen above, for the reproduction 
of a metallic original, two galvanoplastic deposits are re- 
quired, one for the purpose of obtaining a negative, and the 
other in order to produce from the negative the positive — a 
copy true to the original. 

Jacobi, the inventor of galvanoplasty, already endeavored 
to avoid the process of two galvanoplastic deposits by making 
an impression of the original in a plastic mass (melted rosin, 
wax, or plaster of Paris), rendering this non-metallic negative 
conductive, and depositing upon it copper, thus obtaining a 
true copy of the original. 

(558) 



GALVANOPLASTY (rEPKODUCTION). 559 

It is not within the scope of this work to describe the various 
phases through which the art of galvanoplasty has passed 
since its invention. In the historical part reference has been 
made to several facts, such as making non-metallic impressions 
(moulds or matrices) conductive by graphite, a discovery for 
which we are indebted to Murray, and which was also made 
independently by Jacobi ; further, the production of moulds 
in gutta-percha ; so that in this chapter we have solely to deal 
with the present status of galvanoplasty. 

I. Galvanoplasty in Copper. 

Copper is the most suitable metal for galvanoplastic pro- 
cesses, that which is precipitated by electrolysis showing the 
following valuable properties : It can be deposited chemically 
pure, and in this state is less subject to change than ordinary 
commercial copper, or the copper alloys in general use, its 
tensile strength being 20 per cent, greater than that of smelted 
copper. Its hardness is also greater, while its specific gravity 
(8.85) lies between that of cast and rolled copper. 

The physical properties of copper deposited by electrolysis 
are dependent upon the condition of the bath, as well as on 
the intensity and tension of the current. The bath used for 
depositing copper is in all cases, a solution of copper sulphate 
(blue vitriol). 

Smee proved by experiments that, with as intense a current- 
strength as possible without the evolution of hydrogen, the 
copper is obtained as a tenacious, fine-grained deposit. But 
when the current-strength is so intense that hydrogen is 
liberated, copper in a sandy, pulverulent form is obtained, 
and in coarsely crystalline form when the current-strength is 
very slight. 

At a more recent period, Hiibl and Forster have instituted 
a series of systematic experiments for the determination of the 
conditions under which deposits with different physical prop- 
erties are obtained. Forster, in addition, deserves credit for 
his investigations of the anodal solution-processes. 



560 ELECTRO-DEPOSITION OF METALS. 

Hiibl worked with 5 per cent, neutral and 5 per cent, acid 
solutions, as well as with 20 per cent, neutral and 20 per cent, 
acid solutions. The neutral solutions were prepared by boil- 
ing blue vitriol solution with carbonate of copper in excess, 
and the acid solutions by adding 2 per cent, of sulphuric acid 
of 66° Be. The result was that in the neutral 5 per cent, solu- 
tion less brittle deposits were obtained with a slight current- 
density than in a more concentrated solution, though the 
appearance of the deposits was the same. The experiments 
with acidulated baths confirmed the fact that free sulphuric 
acid promotes the formation of very fine-grained deposits even 
with very slight current-densities, and it would seem that the 
brittleness of copper deposited from the acid baths is influ- 
enced less by the concentration than by the current-density 
used. 

With the use of high current-densities, spongy deposits of a 
dark color, but frequently also sandy deposits of a red color, 
are obtained from the neutral as well as from acid blue vitriol 
solutions. These phenomena are directly traceable to the 
effect of the hydrogen reduced on the cathodes. 

However, such spongy deposits are also obtained with the 
use of slight current-densities, when the concentration of the 
electrolyte has become less by the exhaustion of the bath on 
the cathodes, and Mylius and Fromm have shown that copper 
reduced under such conditions had absorbed hydrogen, while 
Lenz, in addition to hydrogen, found in a brittle copper de- 
posit, carbonic oxide and carbonic acid. Soret also found 
carbonic acid in addition to hydrogen, and attributes to it the 
unfavorable effect, while he considers a content of hydrogen 
as unessential for the mechanical properties of the electrolytic- 
ally deposited copper. 

It is impossible to understand where the carbonic acid is to 
come from, provided there has been no contamination of the 
electrolyte by organic substances. 



GALVANOPLASTY (REPRODUCTION). 561 

A. Galvanoplastic Reproduction for Graphic Purposes. 
(Electrotypy. ) 

The processes used in galvanoplasty may be arranged in two 
classes, viz., the deposition of copper with, or without, the use 
of external sources of current, the first comprising galvanoplastic 
deposits produced by means of the single-cell apparatus, and 
the other those by the battery, thermo-electric pile, dynamo 
or accumulator. 

1. Galvanoplastic Deposition in the Cell Apparatus. 

The cell apparatus consists of a vessel containing blue 
vitriol solution kept saturated by a few crystals of blue vitriol 
placed in a muslin bag, or a small perforated box of wood, 
stoneware, etc. In this vessel are placed round or square 
porous clay cells (diaphragms) which contain dilute sulphuric 
acid and a zinc plate, the zinc plates being connected with 
each other and with the objects to be moulded — which may 
be either metallic or made conductive by graphite — by copper 
wire or copper rods. 

The objects to be moulded play the same role as the copper 
electrode in the Daniell cell, and the cell apparatus is actually 
a Daniell cell, closed in itself, in which the internal, instead 
of the external, current is utilized. As soon as the circuit is 
closed by the contact of the objects to be copied with the zinc 
of the porous cell, the electrolytic process begins. The zinc 
is oxidized by the oxygen and with the sulphuric acid forms 
zinc sulphate (white vitriol) while the copper is reduced from 
the blue vitriol solution and deposited in a homogeneous 
layer upon the objects to be moulded. 

Forms of cells. The form and size of the simple cell-appa- 
ratus vary very much according to the purpose for which the 
latter is to be used. While formerly a horizontal arrangement 
of the objects to be copied and of the zinc plates was generally 
preferred, because with this arrangement the fluids show a more 
uniform concentration, preference was later on properly given 
to the vertical arrangement. Particles becoming detached 
36 



562 



ELECTRO-DEPOSITION OF METALS. 



Fig. 135. 



from the zinc plates get only too easily upon the object to be 
reproduced and cause holes in the deposit, while with the 
vertical arrangement the progress of deposition can at any 
time be controlled by lifting out the objects without taking the 
apparatus apart, as in the case with the horizontal arrange- 
ment. Hence, only such apparatus in which the zinc plates 
and the objects to be moulded are arranged vertically oppo- 
site one to the other will here be discussed. 

A simple apparatus frequently used by amateurs for mould- 
ing metals, reliefs, etc., is shown in Fig. 135. 

In a cylindrical vessel of glass or stoneware filled with satu- 
rated blue vitriol solution is placed a porous clay cell, and in 
the latter a zinc cylinder projecting about 0.039 to 0.79 inch 

above the porous clay cell. To 
the zinc is soldered a copper 
ring, as plainly shown in the 
illustration. The clay cell is 
filled with dilute sulphuric acid 
(1 acid to 30 water), to which 
some amalgamating salt may 
be suitably added. The articles 
to be moulded are suspended 
to the copper ring, care being 
had to have the surfaces which 
are to be covered near and 
opposite to the cell. To sup- 
plement the content of copper, 
small linen or sail-cloth bags 
filled with blue vitriol are attached to the upper edge of the 
vessel. 

Large apparatus. — To cover large surfaces, large, square 
tanks of stoneware, or wood, lined with lead, gutta-percha, or 
another substance unacted upon by the bath are used. For 
baths up to three feet long, stoneware tanks are to be preferred. 
Fig. 136 shows the French form of cell apparatus. In the 
middle of the vat, and in the direction of its length, is dis- 




GALVANOPLASTY (REPRODUCTION). 



563 



posed a row of cylindrical cells, close to each other, each pro- 
vided with its zinc cylinder. A thin metallic ribbon is con- 
nected with all the binding screws of the cylinder, and is in 
contact at its extremities with two metallic bands on the 
ledges of the depositing vat. The metallic rods supporting 
the moulds are in contact with the metallic bands of the 
ledges, and therefore, in connection with the zincs. 

Fig. 136. 




The German form of cell apparatus is shown in Fig. 137. 
It is provided with long, narrow, rectangular cells of a corres- 
pondingly greater height than the column of fluid. 

Across the vat are placed three conducting rods connected 
with each other by binding screws and copper wire. To the 
center rod, which lies over the cells, are suspended the zinc 
plates by means of a hook, while the outer two rods serve for 
the reception of the moulds. 

The zinc surfaces in the simple apparatus should be of a 
size about equal to that of the surfaces to be reproduced, if 
dilute sulphuric acid (1 acid to 30 water) is to be used. 



564 



ELECTRO-DEPOSITION OF METALS. 



Copper bath for the cell apparatus. — This consists of a solu- 
tion of 41 to 44 lbs. of pure blue vitriol free from iron, for a 
100-quart bath, with an addition of about 3 \ to 4^ lbs. of 
sulphuric acid of 60° Be., free from arsenic. 

It is not customary to add to the copper bath serving for 
graphic purposes a larger quantity of sulphuric acid than 
that mentioned above, because acid diffuses constantly from 
the fluid in the clay cells into the bath, thus gradually in- 
creasing the content of acid in the latter. If the generation 

Fig, 137. 




of current is induced by acidulating the water in the clay 
cells, a further addition of acid for the cells would actually 
not be required for the progressive development of the current, 
since the acid-residue formed by the decomposition of the 
blue vitriol migrates from the zinc of the cells, and brings 
fresh zinc-ions into solution. A diffusion of acid from the 
cells into the bath would in this manner be avoided, and only 
the zinc-sulphate solution formed would diffuse into the 
copper bath. It appears, however, that without an occasional 
addition of a small quantity of sulphuric acid to the cell- 
solution the process of deposition runs its course very slowly, 
which is not desirable for the manufacture of cliches. 

It may therefore happen that after working the copper bath 



GALVANOPLASTY (REPRODUCTION). 



565 



for a long time, it contains too much acid, a portion of which 
has to be removed. For this purpose the bath was formerly 
mixed with whiting, and the gypsum formed filtered off. This 
method, however, cannot be recommended, gypsum being not 
entirely insoluble in water, and it is better to replace it by 
cupric carbonate or cuprous oxide (cupron). If cupric car- 
bonate be used, it is advisable thoroughly to stir the bath, or 
what is better, to boil it, so as to remove as completely as pos- 
sible the carbonic acid. 

By the diffusion of zinc sulphate solution from the clay 
cells, the bath becomes gradually rich in zinc salt, and it will 
be noticed that a certain limit — with a content of about 10 per 
cent, zinc sulphate — the copper deposits turn out brittle. The 
bath has then to be entirely renewed. 

The content of copper in the bath decreases in accordance 
with the copper deposited, and the concentration of the bath 
would consequently become so low that useful deposits could 
no longer be obtained, if care were not taken to replace the 
copper. This is done by suspending perforated baskets of 
stoneware or lead, filled with blue vitriol crystals, in the bath. 

Since directions are frequently found in which the blue 
vitriol solutions to be used are given according to their weights 
b} r volume or degrees of Be., a table showing the content of 
blue vitriol is given below. 



Degrees Be. 



5° 
10° 
12° 
15° 
16° 
17° 
18° 
19° 
20° 
21° 
22° 




This solution 

contains crystallized 

blue vitriol. 



5 per cent. 

11 " 

13 " 

17 " 

18 " 

19 " 

20 " 

21 " 

23 " 

24 " 

25 " 



566 ELECTRO-DEPOSITION OF METALS. 

Electro-motive force. — The effective electro-motive force in 
the cell apparatus amounts to about 0.75 volt. It may be 
regulated by either bringing the matrices more closely to the 
diaphragms, or removing them a greater distance from them. 
In the first case, the resistance of the bath is decreased, the 
current-density being consequently increased, while in the 
other, the resistance of the bath is increased and the current 
density decreased. 

For regulating the electro-motive force a rheostat may also 
be placed in the circuit, between the matrices and the zincs, 
instead of connecting them directly by a copper wire. Although 
this method is not in vogue, it is certainly recommendable. 

For working on a large scale, the cell apparatus is but sel- 
dom used, at least not for the production of electros. It is, 
however, occasionally employed for the reproduction of ob- 
jects of art with very high reliefs, so as to cover them as uni- 
formly as possible and quite slowly with copper. The cell 
is also still liked for the production of matrices. 

2. Galvanoplastic Deposition by the Battery and Dynamo. 

Since it has been shown in the preceding section that a cell 
apparatus is to be considered as a Daniell cell closed in itself, it 
will not be difficult to comprehend that in economical respects 
no advantage is offered by the production of galvanoplastic 
depositions by a separate battery, because in both cases the 
chemical work is the same, and the zinc dissolved by the use 
of the Daniell or Bunsen cell effects no greater quantity of cop- 
per deposit in the bath than the same quantity of zinc dissolved 
in the cells of the single apparatus. In other respects the use 
of a battery, however, offers great advantages. 

The employment of an external source of current requires 
the same arrangement as shown in Figs. 44 and 45, pp. 140, 
copper anodes being placed in the bath and connected with 
the anode pole of the battery. Copper being dissolved in the 
anodes, the sulphuric acid residue which is liberated is satura- 
ted with blue vitriol, the content of copper being thus, if not 



GALVANOPLASTY (REPRODUCTION). 567 

entirely, at least approximately, kept constant. Furthermore, 
no foreign metallic salts reach the bath, as is the case in the 
simple apparatus, by zinc sulphate solution penetrating from 
the clay cells and causing the formation of rough and brittle 
deposits of copper. With the use of anodes of chemically pure 
copper the bath will thus always remain pure. 

The current may also be regulated within certain limits by 
bringing the anodes more closely to the objects, or removing 
them a greater distance from them. The principal advantage, 
however, consists in that by placing a rheostat in the circuit 
the current strength can be controlled as required by the dif- 
ferent kinds of moulds. 

a. Depositions with the Battery. 

Cells. — The Daniell cell described on p. 71, yields an 
electro-motive force of about 1 volt, and is much liked for this 
purpose. Since the copper bath for galvanoplastic purposes 
requires for its decomposition an electro-motive force of only 
0.5 to 1 volt, it will be best for slightly depressed moulds to 
couple the elements for quantity (Fig. 19, p. 89) alongside of 
each other ; and only in cases where the particular kind of 
moulds requires a current of greater electro-motive force to 
couple two cells for electro-motive force one after the other, an 
excess of current being rendered harmless by means of the 
rheostat, or by suspending larger surfaces. 

Bunsen or Meidinger cells may, however, be used to great 
advantage, since the zincs of the Daniell cells become tarnished 
with copper, and have to be frequently cleansed if the process 
is not to be retarded or entirely interrupted. The Bunsen 
cells need only be coupled for quantity, their electro-motive 
force being considerably greater. To be sure, the running 
expenses are much greater than with Daniell cells, at least 
when nitric acid is used for filling. The lasting constancy of 
the Meidinger cells would actually make them the most suit- 
able of all for continuous working, but by reason of their 
slight current strength a large number of them would have 
to be used. 



5 68 ELECTRO-DEPOSITION OF METALS. 

All that has been said under " Installations with Cells," p. 
132, in regard to conducting the current, rheostats, conduct- 
ing rods, anodes, etc., applies also to plants for the galvano- 
plastic deposition of copper with batteries. 

b. Depositions ivith the Dynamo. 

The improvements in dynamos have also benefited indus- 
trial galvanoplasy, and problems can now be solved in a much 
shorter time and with much greater ease than in a cell appa- 
ratus, without having to put up with the obnoxious vapors 
which make themselves very disagreeably felt in working on 
a large scale with a simple apparatus. That the use of a 
dynamo offers decided advantages is best proved by the fact 
that no galvanoplastic plant of any importance works at 
present without one, and there can scarcely be any doubt that 
establishments which still work exclusively with the simple 
apparatus will be forced to make use of a dynamo, if they 
wish to keep up with competition as regards cheapness and 
rapidity of work. 

Dynamos. — It is best to use a dynamo capable of yielding a 
large quantity of current with an impressed electro-motive 
force of 2, or, at the utmost, 3 volts, in case it is not to serve 
for rapid galvanoplasty; for the latter a machine of 5 to 10 volts 
impressed electro-motive force is required. For the old, slow 
process, by which deposits for graphic purposes are produced 
in 5 to 6 hours, an impressed electro-motive force of 2 volts 
suffices for baths coupled in parallel. If, however, there are to 
be charged from the dynamo one or more accumulator cells, 
which are to furnish current to the bath while the steam engine 
is not running during the intermission of work, or to finish 
deposits after working hours, the impressed electro-motive 
force, with cells coupled in parallel, must be 3 volts, and with 
cells coupled in series in proportion to their number. 

It may also happen that in a galvanoplastic plant currents 
of greatly varying electro-motive force may be required for 
depositions. For depositing copper according to the old pro- 



GALVANOPLASTY (REPRODUCTION). 



569 



cess there should, for instance, be available a large current- 
strength with only 1 to 1.5 volts, while for a rapid galvano- 
plastic bath a current of 6 volts is at the same time to be used. 
If a dynamo of 6 volts impressed electro-motive force, were to 
be used, the excess of electro-motive force would have to be 
destroyed by rheostats in front of the baths requiring a slight 
electro-motive force, in case it is not convenient to couple 
these baths in series (see later on). The destruction of electro- 
motive force is, however, not economical, and, in such a case, 
the use of two dynamos with different electro-motive forces is 
advisable. It is best to combine both dynamos with a motor- 
generator, if the plant is connected with a power circuit of a 

Fig. 138. 




central station, the construction being such that the dynamo 
which is perhaps only temporarily in use can be readily 
disengaged. 

Fig. 138 shows such a double aggregate, built by the firm 
of Dr. G. Langbein & Co. for the German Imperial Printing 
Office. The larger dynamo has a capacity of 1000 amperes 
and 2.5 volts, and the smaller one, one of 250 amperes and 
6 volts. 

Current-conductors of sufficient thickness, corresponding to 
the quantities of current have to be provided to prevent loss 
of current by resistance in the conductors. To avoid repeti- 



570 ELECTRO-DEPOSITION OF METALS. 

tion, we refer to what has been said on this subject under 
"Arrangement of Electro-plating Establishments," the direc- 
tions there given applying also to the galvanoplastic process. 

Coupling the baths. — When coupling the baths in parallel, 
each bath will have to be provided with a rheostat and am- 
meter, while a voltmeter with a voltmeter switch may be em- 
ployed in common for several baths. If the baths are of 
exactly the same composition and the same electrode-distances 
are maintained in them, regulation of the current by the 
shunt rheostat of the dynamo will suffice. 

Coupling the baths in series may under certain conditions 
be of advantage. In such a case, a dynamo of adequately 
higher electro-motive force will of course have to be employed. 

With the baths coupled in series the cathode (object) sur- 
faces in all the baths should be of the same size, or at least 
approximately so. The baths are coupled in series by con- 
necting the anodes of the first bath with the + pole of the 
dynamo, the cathodes of the first bath with the anodes of the 
second, the cathodes of the second with the anodes of the third, 
and so on, and reconducting the current from the cathodes of 
the last bath to the — pole of the dynamo (Fig. 64). 

With this simple coupling in series, the impressed electro- 
motive force is uniformly distributed in all the baths, so that 
with four baths coupled in series, and an impressed electro- 
motive force of 4 volts, an electro-motive force of 1 volt is pre- 
sent in each bath if the conductivity resistance be left out of 
consideration. Hence, it may be readily calculated how many 
baths have to be coupled in series to utilize a given impressed 
electro-motive force, when the electro-motive force required for 
one bath is known. 

If, for instance, there is a dynamo with 6 volts impressed 
electro-motive force, and the electro-motive force required for 
one bath is 1.5 volts, then 4 baths have to be coupled in series, 
since they require 1.5 X 4 = 6 volts. If, however, only one 
volt is required for one bath, then 6 baths will have to be 
coupled in series, or, in case fewer baths are to be used, the 



GALVANOPLASTY (REPRODUCTION). 



571 



impressed electro-motive force of the dynamo has to be suitably- 
regulated by the shunt rheostat. 

Besides, the simple coupling in series, mixed coupling, also 
called coupling in groups, a combination of coupling in parallel 
and in series, may be employed. This is effected by combin- 
ing a number of baths to a group in parallel, and coupling 
several such groups in series. 



Fig. 139. 



4np£Kner£/> 



rt 








RHEOSTAT 




4-^- 










































































(7y 


1LTHETED 





In large galvanoplastic plants the advantages derived from 
this mixed coupling are as follows : 

With the simple couple in series, the electrode-surfaces in 
all the baths must be of the same size. When finished objects 
are taken from a bath, the current conditions are changed, 
until in place of the object taken out fresh surfaces of the same 
size are suspended in the bath, and as this cannot always be 
immediately done, irregularities in working will result. If, 
however, the baths be combined in groups in the manner 
shown in Fig. 139, only the cathode-surfaces of each of the 
groups coupled in parallel, need to be of the same size, or ap- 
proximately so, and with the observation of this condition it 



572 ELECTRO-DEPOSITION OF METALS. 

is entirely indifferent whether a bath of one group is not at 
all charged with cathodes. 

For the adjustment of any difference in the electro-motive 
force in the baths of the separate groups, it is advisable to 
place in each bath a rheostat in shunt. 

While with baths coupled in parallel, the electro-motive 
force of the dynamo corresponds to the requisite electro-motive 
force of one bath, but the current-strength is calculated from 
the sum of all the cathodes present in the different baths, 
with baths coupled in series only the total cathode surface of 
one bath is decisive as regards the current-strength, the electro- 
motive force of the machine resulting from the sum of the 
electro-motive forces of the separate baths. With baths 
coupled in groups the requisite impressed electro-motive force 
is calculated from the number of groups of baths coupled in 
series, but the current-strength from the total cathode-surface 
of only one group. 

The following examples may serve as illustrations : Suppose 
3 baths, each with 100 square decimeters cathode-surface, are 
coupled in parallel, and the electro-motive force for one bath 
is 1.5 volts. Hence in the three baths there are 100 X 3 = 
300 square decimeters cathode surface, and if, for instance, one 
square decimeter requires 2 amperes, then the 3 baths require 
300 X 2 = 600 amperes. Thus the capacity of the dynamo 
must be 600 amperes, with an impressed electro-motive force 
of 1.5 volts, but for practical reasons a machine of 2 volts 
should be selected. 

Suppose 4 baths, each charged with 100 square decimeters 
cathode-surface, are coupled in series, and the bath electro- 
motive force is 1.25 volts, and the current-density 2 amperes. 
Hence there will be required, 100 X 2 = 200 amperes, and 
1.25 X 4 = 5 volts. 

Suppose 9 baths are coupled, mixed in three groups of 3 
baths each, the latter being coupled in parallel, and the three 
groups coupled in series. Now if each group be charged with 
300 square decimeters cathode-surface and the bath electro- 



GALVANOPLASTY (REPRODUCTION). 573 

motive force be also 1.25 volts and the current-density 2 am- 
peres, then there will be required, 300 X2= 600 amperes, 
and 1.25 X 3 = 3.75 volts, or practically, 4 volts impressed 
electro-motive force. 

c. Combined Operation ivith Dynamo and Accumulators. 

When, as is frequently the case in galvanoplastic plants 
working with the slow process of deposition, electrotypes have 
to be finished in a hurry, recourse has to be had to night 
work. If the dynamo is not driven by a motor-generator fed 
from a power circuit of a central station, it will be necessary 
to use for night work either a cell apparatus, or to feed the 
bath from accumulators. 

An interruption in the galvanoplastic deposition of copper 
is a great drawback, because an additional deposit made after 
the current has been interrupted adheres badly upon the one 
previously made, as blisters are readily formed, or the deposit 
peels off. The chief object in the use of an accumulator is 
that it allows of the work being carried on during the noon 
hour when the steam engine is generally stopped, and of fin- 
ishing matrices which are suspended late in the afternoon, 
after working hours. 

In order to avoid repetition, the reader is referred to what 
has been said on p. 184 et seq., in regard to the use of an ac- 
cumulator in addition to the dynamo. 

For galvanoplasty in copper by the slow process, one accu- 
mulator cell of sufficient capacity to supply current for 2 or 3 
hours is, as a rule, all that is required. This cell is charged 
from the dynamo at the same time, while the latter directly 
operates the hath, a machine with an impressed electro-motive 
force of 3 volts being required for the purpose. 

If several cells have to be used, it has to be decided accord- 
ing to the capacity of the dynamo, whether they are to be 
charged in parallel or in series. If great demands are for a 
longer time made on the accumulators, it is advisable to use a 
separate dynamo for charging purposes. 



574 ELECTRO-DEPOSITION OF METALS. 

Copper baths for galvanoplastic depositions with a separate 
source of current. — The directions for the composition of the 
bath vary very much, some authors recommending a copper 
solution of 18° Be., which is brought up to 22° Be. by the 
addition of pure concentrated sulphuric acid. Others again 
increase the specific gravity of the bath up to 25° Be. by the 
addition of sulphuric acid, while some prescribe an addition 
of 3 to 7 per cent, of sulphuric acid. 

It is difficult to give a general formula suitable for all cases, 
because the addition of sulphuric acid will vary according to 
the current-strength available, the nature of the moulds, and 
the distance of the anodes from the objects. The object of 
adding sulphuric acid is, on the one hand, to render the bath 
more conductive and, when used in proper proportions, to 
make the deposit more elastic and smoother, and prevent the 
brittleness and coarse-grained structure which, under certain 
conditions, appear. 

However, it is also the function of the sulphuric acid to 
prevent the primary decomposition of the blue vitriol, and to 
effect in a secondary manner the reduction of the copper. As 
has been explained on p. 50, acids, bases and salts dissociate 
in aqueous solution, and only substances which dissociate 
in aqueous solution are conductors of the electric current, 
they being the better conductors, the greater their power of 
dissociation is. The dilute sulphuric acid being much more 
dissociated, takes charge in a much higher degree of con- 
ducting the current than the less strongly dissociated blue 
vitriol solution. Consequently the cation of the sulphuric 
acid — the hydrogen-ions — migrates to the cathode, and effects 
the decomposition of the blue vitriol, an equivalent quantitj^ 
of copper being reduced upon the cathode. 

The addition of a large quantity of sulphuric acid, as recom- 
mended by some authors, cannot be approved, it having been 
found of advantage only in a few cases. 

For depositing with a battery, somewhat more sulphuric 
acid may for economical reasons be added to the bath than 



GALVANOPLASTY (REPRODUCTION). 575 

when working with the current of a dynamo. The following 
composition has in most cases been found very suitable for the 
reproduction of shallow, as well as of deep, moulds : 

Blue vitriol solution of 19|° Be. 100 quarts, sulphuric acid 
of 66° Be. free from arsenic 4f to 6^ lbs. 

The bath is prepared as follows : Dissolve 48J lbs. of blue 
vitriol in pure warm water, and, to avoid spurting, add gradu- 
ally, stirring constantly, the sulphuric acid. At the normal 
temperature of 59° F. the bath may be worked with a current- 
density of up to 2 amperes, and if the bath be agitated, the 
current-density may be up to 3 amperes. 

Properties of the deposited copper. — As regards elasticity, 
strength and hardness of galvanoplastic copper deposits, Hiibl 
determined that copper of great tenacity, but possessing less 
hardness and strength, is deposited from a 20 per cent, solu- 
tion with the use of a current- density of 2 to 3 amperes. 

For copper printing plates a 20 per cent, solution compounded 
with 3 per cent, sulphuric acid, and current-density of 1.3 
amperes was found most suitable by Giesecke. Dissolve for 
this purpose 50.6 lbs. of blue vitriol for a 100-quart bath and 
add 6.6 lbs. of sulphuric acid. 

Forster and Seidel have shown that the mechanical proper- 
ties of the copper are materially influenced by the temperature 
of the electrolyte. From Forster' s investigations, with a 
cathodal current-density of 1 ampere in an electrolyte com- 
posed of 150 grammes blue vitriol and 50 grammes sulphuric 
acid per liter, it appears that the copper obtained with the 
electrolyte at 140° F., showed the greatest tenacity, it decreas- 
ing again at a higher temperature while the strength slightly 
increased. 

The nature, i. e., the composition, of the electrolyte also 
exerts an influence upon the structure of the deposit. Forster 
compounded the electrolyte previously used with a quantity 
of sodium sulphate equivalent to that of the blue vitriol. 
The result showed that the strength as well as the tenacity 
was unfavorably influenced at a higher temperature. 



576 ELECTRO-DEPOSITION OF METALS. 

Current conditions. — In order to obtain a dense, coherent 
and elastic deposit in the acid copper bath, it is first of all 
necessary to bring the current-strength into the proper pro- 
portion to the deposition-surface, this applying to depositions 
in the simple apparatus, as well as to that produced with an 
external source of current. 

The stronger the sulphuric acid in the clay cells of the 
simple apparatus is, the more rapidly is the copper precipi- 
tated upon the moulds. If the zinc-surfaces of the clay cells 
are very large in proportion to the surfaces of the moulds, 
the deposition of copper also takes place more rapidly. The 
rapid reduction of copper, however, must above all be avoided 
if deposits of desirable qualities are to be obtained, because a 
deposit of copper forced too rapidly turns out incoherent, 
spongy, frequently full of blisters and, with a very strong 
current, even pulverulent. 

The color of the deposit is to some extent a criterion of its 
quality, a red-brown color indicating an unsuitable deposit, 
while a good, useful one may be counted upon when it shows 
a beautiful rose color. 

For filling the clay cells, it has previously been stated that 
the acid is to be diluted in the proportions of 1 part of concen- 
trated sulphuric acid of 66° Be. to 30 parts of water, the zinc 
surface being supposed to be of about the same size as the ma- 
trix-surface. If the zinc-surface should be smaller, stronger 
acid ma}' be used, and if it be larger, the acid may be more 
dilute. The proper concentration of the acid in the clay cells 
is readily ascertained from the progressive result of the deposit 
and its color. 

What has been said in reference to the current-strength ap- 
plies also to the deposition of copper with a separate source of 
current (battery or dynamo). The current-strength must be so 
adjusted by means of a rheostat as to allow of comparatively 
rapid deposition without detriment to the quality of the de- 
posit. 

According to the composition of the bath, a fixed minimum 



GALVANOPLASTY (REPRODUCTION). 



577 



and maximum current-density corresponds to it, which must 
not be exceeded if serviceable deposits are to be obtained. 
There is, however, a further difference according to whether 
the bath is at rest or agitated. Hiibl obtained the following 
results : 





Minimum and maximum current-density 
per 15.5 square inches. 


Blue vitriol solution. 


With solution at 

rest. 

Amperes. 


With solution gently 
agitated. 
Amperes. 


15 per cent, blue vitriol, without 

sulphuric acid ... 
15 per cent, blue vitriol, with 6 

per cent, sulphuric acid . . 
20 per cent, blue vitriol, without 

sulphuric acid 
20 per cent, blue vitriol, with 6 

per cent, sulphuric acid .... 


2.6 to 3.9 
1.5 " 2.3 
3.4 " 5.1 

2.0 " 3.0 






3.9 to 5.2 
2.3" 3.0 
5.1 " 6.8 
3.0 " 4.0 



Touching the addition of sulphuric acid, it was shown that 
no difference in the texture of the deposit is perceptible if the , 
addition of acid varies between 2 and 8 per cent. 

The most suitable current-density for the production of good 
deposits with a bath of the composition given on p. 575, when 
at rest, is for slow deposition 1 to 2 amperes per square deci- 
meter of matrix surface, and when the bath is agitated 2 to 3 
amperes. The current-densities for rapid galvanoplastic baths 
will be given later on. 

Since for ordinary, strongly acid copper baths an electro- 
motive of J, to at the utmost 1 J, volts is required, the more 
powerful Bunsen cells will have to be coupled alongside each 
other, while of the weaker Daniell or Lallande cells, two, or of 
the Meidinger cells, three, will have to be coupled one after 
the other, and enough of such groups have to be combined to 
make their active zinc-surfaces of nearly the same size as the 
surfaces of the matrices. However, for strongly acid baths 
37 



578 ELECTRO-DEPOSITION OF METALS. 

coupling the separate weaker cells alongside each other also 
suffices. 

When all parts of the matrices, as well as the deeper por- 
tions, are covered with copper, the current is weakened in case 
a deposit of a pulverulent or coarse-grained structure appears 
on the edges of the moulds, and it is feared that the deposit 
upon the design or type might also turn out pulverulent. 
The current need not be weakened more than is necessary to 
prevent the dark deposits on the edges from progressing further 
towards the interior of the mould-surfaces. If, by reason of 
too strong a current, pulverulent copper has already deposited 
upon the design or type, and the fact is noticed in time and 
the current suitably weakened, the deposit can generally be 
saved by the layers being cemented together by the copper 
which is coherently deposited with the weaker current. 

In depositing with the dynamo, the current-density and 
electro-motive force have to be properly regulated by means 
of a rheostat. 

Brittle copper deposits may be caused, not only by an unsuit- 
able composition of the electrolyte, improper current-densities 
and impure anodes (see later on), but also by contamination 
of the bath with non-metallic substances, certain organic sub- 
stances especially having an unfavorable effect upon the prop- 
erties of the copper deposit. 

Forster found the use of hooks coated with rubber solution 
in benzol for suspending the cathodes a protection against the 
attacks of the electrolyte and the air, and smooth copper de- 
posits of a beautiful velvety appearance were obtained, but 
they were so brittle that they could not be detached without 
breaking from the basis. The deposit contained small quan- 
tities of carbonaceous substances, which could have been de- 
rived only from a partial solution of the rubber. 

Hiibl also describes the fact of having obtained brittle cop- 
per by the electrolyte having been contaminated by a small 
quantity of gelatine which had passed into solution in the 
preparation of an electrotype upon heliographic gelatine reliefs. 



GALVANOPLASTY (REPRODUCTION). 579 

Dr. Langbein had frequently occasion to notice that baths in 
tanks lined with lead, and provided with a coat of asphalt and 
mastic dissolved in benzol, yielded brittle copper when the 
coat of tlacquer was not perfectly hard, and it was observed 
that by reason of an accidental contamination of the electro- 
lyte with gelatine, deposits were formed which showed the 
branched formation of crystals similar to an arbor Saturni, 
and were extremely brittle. 

Erich Miiller and P. Behntje * have recently investigated 
the effects of such organic additions (colloids) on blue vitriol 
solutions, additions of gelatine, egg albumen, gum, and starch 
being drawn upon for comparing the effects. After an elec- 
trolysis for 15 hours, the deposits obtained from baths com- 
pounded with gum and starch solutions showed no material 
difference in appearance from deposits obtained with the same 
current-strength from pure acidulated blue vitriol solution. 
Deposits obtained from baths to which gelatine and egg 
albumen had been added, however, had lustrous streaks run- 
ning from top to bottom. The weight of these deposits was, 
moreover, greater than that of the copper obtained from pure 
solution, and the presence of gelatine in the deposit could be 
established b}' analysis. Further experiments proved that 
the above-mentioned phenomena were dependent on the 
current-density, and with smaller additions of gelatine, and 
3.5 amperes, thoroughly homogeneous, mirror-bright copper 
coatings could be obtained, thus rendering it possible to pro- 
duce, by an addition of gelatine, a lustrous coppering from 
acid copper baths. The properties of this copper are, however 
such as are not desirable for galvanoplastic purposes. 

It is therefore absolutely necessary to exclude such organic 
substances, even if only dissolved in traces, from contact with 
the electrolyte. 

Duration of deposition. — The time required for the produc- 
tion of a deposit entirely depends, according to what has been 

* Zeitschrift far Elektrochemie, XII, 317. 



580 



ELECTRO-DEPOSITION OF METALS. 



said on p. 124, on the current-density used. One ampere de- 
posits in one hour 1.18 grammes of copper, and from this, 
when the current-density is known, the thickness acquired by 
the deposit in a certain time can be readily calculated,. 

A square decimeter of copper, 1 millimeter thick, weighs 
about 89 grammes, and to produce this weight with 1 ampere 
current-density, there are required - 8 t 9 tV°- == 75 hours. By tak- 
ing the thickness of a deposit as 0.18 millimeter, which suf- 
fices for all purposes of the graphic industry, then 1 square 
decimeter will weigh 89 X 0.18 = 16.02 grammes, and for 
their deposition with 1 ampere current-density will be re- 
quired', in round numbers, xnf= 13-J- hours. 

Below is given the duration of deposition for electrotypes 
0.18 millimeter thick with different current-densities, and in 
addition the time is stated which would be required for the 
formation of a deposit 1 millimeter thick, so that the calcula- 
tion of the time required for depositing a copper film of a 
thickness different from 0.18 millimeter can be readily made 
by multiplying the number of hours in the third column by 
the desired thickness of the copper. 



With a current-density of 


Duration of deposition for 
0.18 millimeter thick- 
ness of copper 


A deposit of 1 millimeter 
thickness requires 


0.5 ampere 


27 


hours 


150* 


hours 


0.75 " 


18 


a 


101'J 


" 


1.0 


13i 


a 


75 


u 


1.5 


9 


<; 


50 


'• 


20 


6| 


" 


37J 


It 


2.5 


5* 


• '( 


30 


11 


3.0 


4* 


it 


25 


" 


4.0 


3f 


1 1 


18| 


" 


5.0 


2| 


a 


15 


" 


6.0 


2\ 


(i 


12 J 


" 


7.0 " 


2 


it 


lOf 


cc 


8.0 " 


ItV 


it 


9* 


u 


9.0 " 


1* 


a 


8J 





Nitrate baths. — To shorten the duration of deposition, baths 



GALVANOPLASTY (REPRODUCTION). 581 

have been recommended which, in place of blue vitriol, are 
prepared with cupric nitrate, and which by reason of being 
more concentrated will bear working with greater current- 
densities. To further increase their conducting power, ammo- 
nium chloride is added. Independent of the fact that de- 
posits obtained in these baths are inferior in quality to those 
produced in blue vitriol baths, such baths require frequent 
corrections, they becoming readily alkaline in consequence of 
the formation of ammonia. Besides, in view of the short 
time required for deposition by the rapid galvanoplastic pro- 
cess, there is no necessity for nitrate baths. 

Agitation of the baths. — From Hiibl's table it will be seen 
that a copper bath in motion can bear considerably higher 
current-densities, and hence will work more rapidly than a 
bath at rest. In electrolytically refining copper it was found 
that, if the process of reducing the copper is to proceed in an 
unexceptional manner, the bath must be kept entirely homo- 
geneous in all its parts. "When a copper bath is at rest, and 
the operation of deposition is in progress, the following pro- 
cess takes place : The layers of fluid on the anodes having by 
the solution of copper become specifically heavier, have a 
tendency to sink down, while layers of fluid which have be- 
come poorer in copper, and consequently specifically lighter, 
rise on the cathodes to the surface. These layers contain 
more sulp*huric acid than the lower ones, hence their resist- 
ance is slighter and their conducting power greater, the latter 
being still further increased by the layers heated by the cur- 
rent also rising to the surface. In consequence of this process 
there will be a variable growth in thickness of the deposit, 
and various phenomena may appear which, according to the 
composition of the layers in question, can be theoretically 
established. If the intermixture of the electrolyte has not 
progressed to any great extent, and thus there are no great 
differences, as regards composition, between the upper and 
lower layers of the fluid, the deposit will be quite uniformly 
formed upon the lower as well as upon the upper portions of 



582 ELECTRO-DEPOSITION OP METALS. 

the cathodes, although it will be somewhat thicker on the 
lower portions, which dip into the more concentrated copper 
solution, than on the upper portions. This difference in 
thickness in favor of the lower cathode-surfaces will become 
more pronounced as the concentration of the lower layers of 
the fluid increases, while the growth in thickness on the upper 
cathode-surface is kept back. The concentration of the upper 
layers of fluid may finally happen to become so slight that the 
hydrogen-ions do not meet with sufficient blue vitriol for de- 
composition, and hydrogen will consequently be separated 
and the formation of a sandy or spongy deposit noticed. 

It may, however, also happen that a current of slight electro- 
motive force cannot overcome the greater resistance of the 
more concentrated lower layers of fluid, and in consequence 
passes almost exclusively through the upper layers. So long 
as the hydrogen-ions find sufficient blue vitriol and the cur- 
rent-density is slight, the growth of the deposit on the upper 
cathode-surfaces may, in this case, progress, while it comes to 
a stand-still on the lower ones. 

Experiments by Sand * have shown that in consequence of 
local exhaustion of blue vitriol in an acid copper bath more 
than 60 per cent, of the current is, notwithstanding natural 
diffusion, consumed for the evolution of hydrogen. The pro- 
duction of serviceable deposits under such conditions is of 
course impossible. 

By constant agitation of the bath, the layers poorer in metal, 
which have deposited copper on the cathodes, are rapidly re- 
moved, and layers of fluid richer in metal are conveyed to the 
cathodes, the greatest possible homogeneity of the bath being 
thus effected, and the operation of deposition becoming 
uniform. 

Baths in motion show less inclination to the formation of 
buds and other rough excrescences, and hence the current- 
density may be greater than with solutions at rest, the result 

* Zeitschrift fur physikalishe Chemie, xxxv, 641. 



GALVANOPLASTY (REPRODUCTION). 583 

being that deposition is effected with greater rapidity. These 
experiences gathered in electro-metallurgical operations on a 
large scale, have been advantageously applied to galvano- 
plasty. 

Stirring contrivances. — Constant agitation of the copper bath 
may be effected in various ways. A mechanical stirring con- 
trivance may be provided, or agitation may be effected by 
blowing in air, or finally, by the flux and reflux of the copper 
solution. 

With the use of a stirring apparatus, stirring rods of hard 
rubber or glass which are secured to a shaft running over the 
bath, swing like pendulums, between the electrodes. This 
motion of the shaft is effected by means of leverage driven 
from a crank pulley. The stirring rods should not move 
with too great rapidity, otherwise the slime from the anodes, 
which settles in the bath, might be stirred up. 

Agitation of the bath has also been effected by slowly re- 
volving, by means of a suitable mechanism, cast copper anodes 
of a square cross-section, this mode of motion having the 
advantage of very thoroughly mixing the electrolyte without 
being too violent. 

If the bath is to be agitated by blowing in air, the latter is 
forced in by means of a pump through perforated lead pipes, 
arranged horizontally about two inches from the bottom of 
the tank. 

It is best to use a small air compressor in connection with 
an air chamber provided with a safety valve. The quantity 
of air to be conveyed to the perforated lead pipes is regulated 
by means of a cock or valve. The number and size of the per- 
forations in the lead coil must be such that the air passes out 
as uniformly as possible the entire length of the pipe, so that 
all portions of the electrolyte are uniformly agitated. For 
smaller baths an ordinary well-constructed air-pump suffices 
for pressing in the air. 

Agitation of the bath by flux and reflux of the solution 
may be effected in various ways, and is especially suitable 
where many copper baths are in operation. 



584 



ELECTRO-DEPOSITION OF METALS. 




The baths are arranged in 
the form of steps. Near the 
bottom each bath is provided 
with a leaden outlet-pipe (Fig. 
140), which terminates above 
the next bath over a distribut- 
ing gutter, or as a perforated 
pipe, h. From the last bath the 
copper solution flows from a 
reservoir, E, from which it is 
forced by means of a hard- 
rubber pump, i, into the reser- 
voir, A, placed at a higher 
level. From A it again passes 
through the baths, B, C and D. 
A leaden steam -coil may, if 
necessary, be placed in A, to 
increase the temperature, if it 
should have become too low. 
Over A a wooden frame cov- 
ered with felt may be placed ; 
the copper solution flowing 
upon the frame and passing 
through the felt, is thereby 
filtered. 

While agitation of the bath 
presents great advantages, there 
is one drawback connected with 
it, which, however, should not 
prevent its adoption. With 
baths at rest, dust and insolu- 
ble particles becoming detached 
from the anodes sink to the 
bottom and have no injurious 
effect upon the deposit. On 
the other hand, in agitated 



GALVANOPLASTY (REPRODUCTION). 585 

baths, they remain suspended in the electrolyte, and it may 
happen that they grow into the deposit, giving rise to the for- 
mation of roughnesses (buds). Everywhere that such rough- 
ness is formed, it increases more rapidly in proportion to the 
other smooth portions of the cathode, and these excresences 
frequently attain considerable thickness, which is not at all 
desirable. 

It is, therefore, advisable to make provision for keeping 
such baths perfectly clean. Baths agitated by flux and 
reflux can be readily filtered, as described above, previous 
to their passing into the collecting reservoir. Solutions agi- 
tated by a stirring contrivance, or by blowing in air, should 
be occasionally allowed to rest and settle. The perfectly clear 
solution is then siphoned off, and the bottom layers are freed 
from insoluble particles by filtering. With the use of impure 
anodes, which, however, cannot be by any means recom- 
mended, it is best to sew them in some kind of fabric, for in- 
stance, muslin, the fibers of which have been impregnated 
with ethereal paraffine solution to make them more resistant 
towards the action of the sulphuric acid. In order to keep 
the electrolyte as clean as possible, it is best to treat chem- 
ically pure anodes in the same manner. 

In case no means for agitating the bath should be available, 
good results may, according to Maximowitsch, be obtained by 
the following arrangement : The electrodes are placed hori- 
zontally and in such a manner that in the bath the anodes are 
over the cathodes. The new solution is thus formed in the 
upper portions of the bath on the anodes and being specifically 
heavier than the old exhausted solution sinks to the bottom 
where it displaces the exhausted solution poor in copper, the 
latter being by reason of its slighter specific gravity forced up- 
wards. Hence, without the use of any mechanical contriv- 
ance the freshly-formed solution is constantly mixed with the 
old solution. 

To prevent small particles of metal from the anodes falling 
upon the cathodes and there giving rise to the evolution of gas, 



586 ELECTRO-DEPOSITION OF METALS. 

a frame filled with unbleached, undyed silk is placed between 
the two electrodes. 

For the production of a beautiful, dense and firm deposit, 
according to this process, Schonbeck recommends the follow- 
ing bath: Crystallized blue vitriol 125 lbs., concentrated sul- 
phuric acid 12J lbs., water 500 lbs. 

Current- density per square decimeter electrode surface 6 to 10 
amperes ; electro-motive force for every ampere 0.8 volt ; electrode 
distance 8 centimeters. 

Anodes. — Annealed sheets of the purest electrolytic copper 
should be suspended in the bath. Impure anodes introduce 
other metallic constituents into the bath, and the result might 
be a brittle deposit. The use of old copper boiler sheets, so 
frequently advocated, is decidedly to be rejected. 

The more impurities the anodes contain, the darker the 
residue formed upon them will be, and this residue in time 
deposits as slime upon the bottoms of the tanks. Anodes of 
electrolytically deposited, and therefore perfectly pure, copper 
also yield a residue, which, however, is of a pale brown ap- 
pearance, and consists of cuprous oxide and metallic copper. 
It is recommended daily to free the anodes from adhering 
residues by brushing, so as to decrease the collection of slime 
in the bath. The anodes of baths in motion are best sewed, as 
above described, in a close fabric to retain insoluble particles. 

In connection with his previously mentioned experiments, 
Forster ascertained that with the use of ordinary copper, at 0.3 
ampere current-density, about 7.4 grammes (4.15 drachms) of 
red-brown anode slime with 60 to 70 per cent, of copper, par- 
tially in the form of cuprous oxide, were at the ordinary tem- 
perature obtained from 6.6 lbs. of anode copper. On the other 
hand, at a temperature of 104° F., only 24 grammes (1.25 
drachms) of a pale gray slime consisting chiefly of silver, lead, 
lead sulphate and antimony combinations with only a slight 
content of copper were under otherwise equal conditions ob- 
tained. By raising the temperature of the electrolyte to 140° 
F. the quantity of anode slime increased considerably, and at 



GALVANOPLASTY (REPRODUCTION). 587 

1 ampere current-density amounted to about twenty times as 
much. The slime, in addition to a smaller quantity of the 
above-described pale gray slime, contained larger quantities of 
well-formed lustrous copper crystals which could scarcely be 
derived from the rolled copper anodes. Wohlwills made 
analogous observations in the electrolysis of gold chloride 
solution containing hydrochloric acid, and based upon these 
observations, Forster assumes that at the higher temperature 
the anode copper sends forth augmented univalent cuprous- 
ions into the copper solution, the cuprous sulphate solution 
formed being decomposed to cupric sulphate (blue vitriol) 
while copper is separated, according to the following equation : 

Cu 2 S0 4 = CuSO, + Cu. 

Cuprous sulphate. Cupric sulphate. Copper. 

The anode surfaces should be at least equal to that of the 
moulds, and for shallow moulds the distance between them and 
the anodes may be from 2 to 3 inches, but for deeper moulds 
it must be increased. 

Tanks. — Acid-proof stoneware tanks serve for the reception 
of the acid copper baths, or for larger baths, wooden tanks 
lined with pure sheet-lead about 0.11 to 0.19 inch thick, the 
seams of which are soldered with pure lead. It should be 
borne in mind that a coat of lacquer, as previously men- 
tioned, may have an injurious effect. 

Rapid galvanoplasty. Thus far galvanoplastic baths with 
an average content of 22 per cent, of blue vitriol and 2 to 3 
per cent, of sulphuric acid have only been referred to. Such 
baths were exclusively used up to the end of 1899. The 
current-density employed in practice amounted to scarcely 
more than 25 amperes, and the customary thickness of 0.15 
to 0.18 millimeters for electrotypes was at the best attained in 
4| to 5 hours. 

The much-felt want of producing galvanoplastic deposits of 
sufficient thickness in a materially shorter time gave rise to 
search for ways and means to attain this object. 



588 ELECTRO-DEPOSITION OF METALS. 

Taking into consideration the fact that a larger quantity of 
copper can in a shorter time be deposited with the use of 
higher current-densities, the conditions under which the use 
of higher current-densities becomes possible without leading 
to the reduction of a useless, brittle or pulverulent deposit 
had to be ascertained. By the investigations of Hiibl it had 
been shown that the production of good deposits is by no 
means dependent on a high content of sulphuric acid in the 
electrolyte, but that acidulating the copper bath only so far as 
to prevent the formation of basic salts suffices. 

It was further known that by the bath containing a large 
quantity of sulphuric acid, the solubility of blue vitriol is de- 
creased, and since good deposits can with high current- 
densities be obtained only from highly-concentrated blue 
vitriol solutions, the reduction of the content of sulphuric 
acid became an absolute necessity. 

There is, however, still another reason why copper baths 
working with high current-densities can only be compounded 
with small quantities of sulphuric acid. It has previously 
been mentioned that the sulphuric acid is dissociated into 
hydrogen-ions and S0 4 -ions, and that hydrogen-ions effect 
the reduction of copper in a secondary manner. By a small 
addition of sulphuric acid, this secondary reduction is to be 
largely avoided, and the copper is to be brought to separate 
chiefly in a primary manner, because by reason of the 
accelerated process of reduction at high current densities, 
there is danger of hydrogen-ions being brought to separate as 
h} r drogen gas on the cathodes, which might give rise to the 
formation of a sandy or spongy deposit. 

In a 20 per cent, blue vitriol solution compounded with 1 
per cent, of sulphuric acid, the copper solution and the sul- 
phuric acid participate equally, according to Hiibl, in con- 
ducting the current ; while with a content of 5 per cent, of 
acid, the conduction of the current is almost exclusively taken 
charge of by the acid-ions. Thus, the smaller the content of 
free sulphuric acid, the greater the quantity of primarily de- 



GALVANOPLASTY (REPRODUCTION). 589 

posited copper will be, and the less the danger of hydrogen- 
occlusion, or the formation of a hydrate. 

However, a smaller content of sulphuric acid in the electro- 
lyte, together with a greater content of blue vitriol, is by itself 
not sufficient for removing the possibility of the formation of 
spongy deposits caused by the layers of fluid on the cathode 
having become poorer in metal. Provision has to be made 
for the vigorous agitation of the electrolyte, so that the layers 
poor in metal on the cathode are constantly replaced by layers 
richer in metal, a discharge of hydrogen-ions on the cathodes 
being thus best prevented ; and coherent copper-deposits of 
great hardness and sufficient tenacity for graphic purposes are 
even with very high current-densities obtained. 

This process, based upon the principles above mentioned, 
was perfected in 1900, and the term rapid galvanoplasty has 
been applied to it. 

It is obvious that the term rapid galvanoplastic bath cannot 
be claimed solely for one composition, but that all acid copper 
baths which yield deposits in a materially shorter time than 
was formerly possible may thus be designated. According to 
the objects the rapidly-working baths are to serve, it would 
even be rational that their compositions should vary, as will 
be directly seen. 

While shallow impressions, for instance, autotypes, wood- 
cuts, etc., only require a very small addition of sulphuric acid, 
for deep impressions of set-up type a larger content of sulphuric 
acid is necessary, especially when the type has been set with 
low spaces. For the reproduction of moulds of objects of art 
in very high relief, rapid galvanoplasty is only within certain 
limits applicable. 

Below will be given two compositions of rapid galvanoplastic 
baths, which are considered the highest and lowest limits, 
though it is not to be understood that good results cannot be 
obtained with baths containing more or less blue vitriol and 
sulphuric acid. These two baths, however, have proved re- 
liable in practical rapid galvanoplasty, and the necessity for 
other compositions will scarcely arise. 



590 ELECTRO-DEPOSITION OF METALS. 

For shallow impressions of autotypes, wood-cuts, etc. — In a 
100 quart bath : 74.8 lbs. of blue vitriol, 0.44 lb. of sulphuric 
acid of 66° Be. 

Dissolve the blue vitriol with the assistance of heat. 

This bath being oversaturated with blue vitriol, crystals 
would be formed, which must by all means be avoided, and 
for this purpose the bath has to be constantly kept at a tem- 
perature of about 78.8° to 82.4° F. At this temperature the 
bath shows about 25° Be., and at 64.4° F., 27° Be. 

Heating the bath is best effected by means of a lead coil on 
the bottom of the lead-lined tank, through which steam is 
introduced until the bath shows the desired temperature. 
Since, by reason of the high current-densities, the temperature 
of the bath is still further increased, which might be detri- 
mental with the use of wax moulds, the lead coil should be 
furnished with an additional branch for the introduction of 
cold water in case the temperature becomes excessive. 

It is not likely that a larger bath of the above-mentioned 
composition will cool off enough over night for the crystalliza- 
tion of blue vitriol, especially if it is covered and the work- 
room is not exceedingly cold. There is danger of the crystal- 
lization of blue vitriol if the work-room is not kept at an even 
temperature, or the bath is not worked for one or more days 
in succession. In the latter case it is advisable, the evening 
before work is stopped, to heat the bath more than usual and 
dilute it with water. The quantity of the latter which has to 
be added to make up what may in a certain time be lost by 
evaporation will soon be learned by experience. If, for the 
sake of precaution, the bath is covered, it will be found ready 
for work when operations are resumed. 

In order to obtain deposits of good quality with high current- 
densities, vigorous agitation of the bath is required. This is 
most uniformly effected by blowing in air by means of an air 
compressor. The bath may also be agitated, though less uni- 
formly so in all portions, b} r means of a copper paddle fitted 
to the front of the tank and driven bv means of a band from 



GALVANOPLASTY (REPRODUCTION). 591 

a transmission. It is placed about six inches above the bot- 
tom of the tank and, the paddles being set at an angle of 45°, 
a vigorous motion of the lower layers towards the surface is 
effected. 

If the above-mentioned conditions be observed, the current- 
dendty for this bath may amount up to 6 amperes per square 
decimeter, and with a distance of about 6 centimeters of the 
cathodes from the anodes, the electro-motive force will ap- 
proximately be 6 volts. When working on an average with 
6 amperes per square decimeter, a deposit of 0.15 millimeter 
thick will in this bath be obtained in 1J to If hours. 

With the use of gutta-percha matrices, the bath may be 
somewhat more heated than when working with wax moulds, 
and still higher current-densities than those given above may 
be employed, the deposit being then finished in a still shorter 
time. It is, however, advisable not to carry the work of the 
current to an excess, otherwise the copper might readily show 
properties not at all desirable. 

It may, under certain circumstances be advantageous, nay 
even necessary, to face the black-leaded matrices with copper 
at a somewhat slighter current-density, while the bath is at 
rest, i. e., not agitated by a stirring contrivance, or by blow- 
ing in air, and to resume agitation and increase the current- 
strength only after the matrices are coated with copper. 
Thus, according to the size of the galvanoplastic plant, it ma} 7 
be desirable to have a smaller coppering bath not furnished 
with a stirring contrivance, from which the matrices, after 
having been faced with copper, are transferred to the agitated 
bath. 

It may here be remarked that Knight's process of coppering 
the matrices with neutral blue vitriol solution and iron fil- 
ings, which is much liked, is not applicable in rapid galvano- 
plasty. In suspending such matrices coated with copper in 
the rapid bath, the slight copper-film is, so to say, burnt, and 
a proper deposit can no longer be effected. 

In a bath of the composition given above, it is sometimes 



592 ELECTRO-DEPOSITION OF METALS. 

difficult to obtain with the above-mentioned high current- 
densities unexceptionable electrotypes from matrices produced 
from deep and steep set-up type. The shallow portions, to be 
sure, copper well, but the copper does not spread into the 
deeper portions, and holes are left. By the addition of certain 
substances, for instance, alcohol, this drawback can, to be sure, 
be somewhat improved, but not entirely removed, and for this 
reason such matrices are further worked in a bath, the compo- 
sition of which is given below. It is, however, preferable to 
preparatively copper such type-compositions, especially when 
low spaces have been used, and after about \ hour to transfer 
the matrices to the rapid galvanoplastic bath. By working in 
this manner, the electrotypes will be free from holes, and fin- 
ishing even the largest customary forms will not require more 
than 2 hours. 

For deep impressions. — In a 100-quart bath : 57.2 lbs. of blue 
vitriol, 1.76 lb. of sulphuric acid. 

It is recommended not to deposit at a lower temperature of 
the bath than 68° F., though with this concentration the 
danger of crystallization is less. For heating and cooling the 
electrolyte, a lead coil, as previously described, is advantage- 
ously used, and provision for thorough agitation has to be 
made. This bath is generally allowed to work with 4.5 to 5 
amperes current-density, the electro-motive force, with a dis- 
tance of 6 centimeters of the anodes from the cathodes, amount- 
ing then to about 4| volts. The copper deposit attains in 2^ 
hours a thickness of 0.15 millimeter, and in 2£ hours one of 
0.18 millimeter. Higher current-densities are also permis- 
sible, and the operator will soon find out how far he can go in 
this respect. 

Deeper forms become well covered, especially if, according 
to Rudholzner's proposition, about 1 lb. of alcohol is added. 
But, nevertheless, it is recommended to preparatively copper 
in the ordinary acid copper bath impressions of very steep 
set-up type with low spaces, as with the use of high current- 
densities the streaks which are temporarily formed upon 



GALVANOPLASTY (REPRODUCTION). 593 

the printing faces of the electrotypes are thus most surely 
avoided. 

Heating the baths may be omitted in plants lacking the 
necessary contrivances. The blue vitriol solution must then 
be of such a composition as to preclude all danger of blue 
vitriol crystallizing out even at the lowest temperature of the 
work-room. Somewhat lower current-densities corresponding 
to the slighter concentration have of course to be used. 

Regarding the quality of the copper deposit effected with 
high current-densities, it may be said that its tenacity is good, 
'better in the second bath than in the one first mentioned, but 
in all cases sufficient for the electrotypes. The copper is how- 
ever, decidedly somewhat harder than that deposited from the 
ordinary baths as proved by its slight wear in printing. 

The treatment of the rapid galvanoplastic baths will be 
readily understood from what has been said above. On the 
one hand, the baths must not be allowed to cool to a tempera- 
ture at which the blue vitriol would no longer be held in 
solution, but would crystallize ; and, on the other, the reaction 
has from time to time to be tested with red congo paper which 
must acquire a plainly-perceptible blue color. If such is not 
the case, no, or too little, free sulphuric acid is present in the 
bath, and brittle deposits will be formed which cannot be de- 
tached whole from the matrices. When this is noticed add 
0.44 lb. of sulphuric acid per 100 quarts of bath, or 1.76 lb. 
to the bath for deep impressions. 

The excess of acid is very rapidly consumed with the use of 
copper plates which have been electrically deposited and, 
without recasting and rolling, suspended as anodes in the 
bath. The use of rolled anodes is therefore absolutely neces- 
sary, and, as previously described, they should be sewed in a 
close fabric to avoid contamination of the bath by the anode- 
slime formed, and by small copper crystals. 

Special attention should be paid to furnish the matrices with 
conductors of sufficiently large cross-section corresponding to 
the great current-strengths. This will later on be referred to. 
38 



594 ELECTRO-DEPOSITION OF METALS. 

Examination of the Acid Copper Baths. 

The copper withdrawn from the bath by deposition is only 
partially restored, but not entirely replaced, by the anodes, 
and hence the content of copper will in time decrease, and the 
content of free acid increase. The deficiency of copper can, 
however, be readily replaced by suspending bags filled with 
blue vitriol in the bath, while too large an excess of acid is 
removed by the addition of copper carbonate or cuprous oxide 
(cupron). 

However, in order not to grope in the dark in making such 
corrections of the bath, it is necessary to determine from time' 
to time the composition of the copper solution as regards the 
content of copper and acid, for which purpose the methods 
described below may be used. 

Determination of Free Acid. — The free acid is determined by 
titrating the copper solution with standard soda solution, 
congo-paper being used as an indicator. Bring by means of a 
pipette, 10 cubic centimeters of the copper bath into a beaker, 
dilute with the same quantity of distilled water, and add drop 
by drop from a burette standard soda solution, stirring con- 
stantly, until congo-paper is no longer colored blue when 
moistened with a drop of the solution in the beaker. Since 1 
cubic centimeter of standard soda solution is equal to 0.049 
gramme of free sulphuric acid, the cubic centimeters of stand- 
ard soda solution used multiplied by 4.9 give the number of 
grammes of free sulphuric acid per liter of bath. 

Volumetric determination of the content of copper according to 
Haen's method. — This method is based upon the conversion of 
blue vitriol and potassium iodide into copper iodide and free 
iodine. By determining the quantity of separated free iodine 
by titrating with solution of sodium hyposulphite of known 
content, the content of blue vitriol is found by simple calcu- 
lation. The process is as follows : Bring 10 cubic centimeters 
of the copper bath into a measuring flask holding -^ liter, 
neutralize the free acid by the addition of dilute soda lye until 
a precipitate of bluish cupric hydrate, which does not disap- 



GALVANOPLASTY (REPRODUCTION). 595 

pear even with vigorous shaking, commences to separate. 
Now add, drop by drop, dilute sulphuric acid until the pre- 
cipitate just dissolves ; then fill the measuring flask up to the 
mark with distilled water, and mix by vigorous shaking. Of 
this solution bring 10 cubic centimeters by means of a pipette 
into a flask of 100 cubic centimeters' capacity and provided 
with a glass stopper ; add 10 cubic centimeters of a 10 per 
cent, potassium iodide solution ; dilute with some water, and 
allow the closed vessel to stand about 10 minutes. Now add 
from a burette, with constant stirring, a decinormal solution 
of sodium hyposulphite until starch-paper is no longer colored 
blue by a drop of the solution in the flask. Since 1 cubic 
centimeter of decinormal solution corresponds to 0.0249 
gramme of blue vitriol (= 0.0003 gramme of copper), the 
content of blue vitriol in one liter of the solution is found by 
multiplying the number of cubic centimeters of decinormal 
solution used by 24.9. For the correctness of the result it is 
necessary that the copper bath should be free from iron. 

The electrolytic determination of the copper being more simple, 
it is to be preferred to the volumetric method. Bring by 
means of the pipette 10 cubic centimeters of the copper bath 
into the previously weighed platinum dish, add 2 cubic centi- 
meters of strong nitric acid, fill the dish up to within 1 centi- 
meter of the rim with distilled water, and electrolyze with a 
current-strength ND 100 = 1 ampdre. 

Deposition of copper is finished when a narrow strip of 
platinum sheet placed over the rim of the dish and dipping 
into the fluid shows in 10 minutes no trace of a copper de- 
posit, which is generally the case in 3J hours. The deposit 
is then washed without interrupting the current, rinsed with 
alcohol and ether, and dried for a short time at 212° F. in 
the air-bath. The increase in weight of the platinum dish 
multiplied by 100 gives the content of metallic copper in 
grammes per 1 liter of bath. To find the content of blue 
vitriol, multiply the found content of copper per liter by 3.92, 
or multiply the content of copper determined in 10 cubic 
centimeters of bath by 3.92. 



596 ELECTRO-DEPOSITION OF METALS. 

If now the content of free acid and of the blue vitriol in the 
bath has been ascertained, a comparison with the contents 
originally present in preparing the bath will show how many 
grammes per liter the content of acid has increased, and how- 
many grammes the content of copper has decreased. Then 
by a simple calculation it is found how much dry pure copper 
carbonate has to be added per liter of solution to restore the 
original composition. For each gramme more of sulphuric 
acid than originally present, 1.26 grammes of copper carbon- 
ate have to be added, and each gramme of copper carbonate 
increases the content of blue vitriol 2.02 grammes per liter of 
bath. By reference to these data the operator is enabled to 
calculate whether the quantity of copper carbonate added for 
the neutralization of the excess of free acid suffices to restore 
the original content of blue vitriol, or whether, and how 
much, blue vitriol per liter has to be added. 

With the use of baths in which the solutions circulate, the 
additions are best made in the reservoir placed at a higher 
level, into which the solution constituting the bath is raised 
by means of a pump. The composition of such baths, con- 
nected one with the other, is the same, and a single determi- 
nation of the content of copper and free sulphuric acid will 
suffice. However, with baths, the contents of which do not 
circulate and are not mixed, a special determination has to be 
made for each bath, and the calculated additions have to be 
made to each separate bath. 

Operations in Galvanoplasty for Graphic Purposes. 

The manipulations for the production of galvanoplastic 
deposits for printing books and illustrations will first be 
described. 

1. Preparation of the moulds (matrices) in plastic material. 
If a negative of the original for the production of copies is 
not to be made by direct deposition upon a metallic object, 
it has to be prepared by moulding the original either in a 
plastic mass which, on hardening, will retain the forms and 



GALVANOPLASTY (REPRODUCTION). 597 

lines of the design to the finest hatchings, or in a material, 
which plastic itself, retains the impression unaltered. Suitable 
materials for this purpose are : Gutta-percha, wax (stearine, 
etc.), and lead. 

The preparation of moulds in gutta-percha and wax will first 
be described, and the production of metallic matrices will be 
referred to in the next section. 

a. Moulding in gutta-percha. — For the reproduction of the 
fine lines of a wood-cut or copper-plate, pure gutta-percha, 
freed by various cleansing processes from the woody fibers, 
earthy substances, etc., found in the crude product, is very 
suitable. Besides the requisite degree of purity, the gutta- 
percha should possess three other properties, viz., it must 
become highly plastic by heating, without, however, becoming 
sticky, and finally it should rapidly harden. 

The most simple way of softening gutta-percha is to immerse 
it in water of 170° to 190° F. When thoroughly softened no 
hard lumps should be felt on kneading with the hands, which 
should be kept thoroughly moistened with water during the 
operation. A fragment of the gutta-percha corresponding to 
the size of the object to be moulded is then rolled into a plate 
about £ to f inch thick. To facilitate the detachment of the 
mould after cooling, the surface of the gutta-percha which is 
to receive the impression should be well brushed with black- 
lead (plumbago or graphite), an excess of it being removed by 
blowing. 

The original (wood-cut, autotype, set-up type, etc.) must be 
firmly locked in the usual manner, and the surface is then 
cleansed from dirt and stale ink by brushing with benzine. 
When dry it is brushed over with plumbago, an excess of it 
being removed by means of a bellows. 

The black-leaded surface of the warm gutta-percha plate is 
then placed upon the black -leaded face of the original, and 
after gently pressing the former with the hand upon the latter, 
the whole is placed in the press. 

b. Moulding in wax. — Beeswax is a very useful material for 



598 ELECTRO-DEPOSITION OF METALS. 

preparing moulds, but, like stearine, it is according to the 
temperature now softer and now harder, which must be taken 
into consideration. In the cold state pure beeswax is quite 
brittle, and apt to become full of fissures in pressing. To 
decrease the brittleness certain additions are made to the wax ; 
various formulas for such compositions recommended by dif- 
ferent authors are here given : 

a. White wax 120 parts, stearin 50, tallow 30, Syrian 
asphalt 40, elutriated graphite 5. (G. L. von Kress). 

b. Yellow beeswax 700 parts, paraffin 100, Venetian tur- 
pentine 55, graphite 1 75 ; or, cake wax 50 parts, yellow wax 
50, ceresin 15, Venetian turpentine 5. (Karl Kempe). 

c. Wax 20 parts, thick turpentine 20, rosin 10, graphite 50. 
(Hackewitz). By reason of its large content of graphite, this 
composition which is excellent in every respect, can be 
recommended for taking moulds from objects which can be 
black-leaded only with difficulty. 

d. Yellow wax 900 parts, Venetian turpentine 135, graphite 
22. (Urquhart). 

e. Pure beeswax 850 parts, crude turpentine 100, elutri- 
ated graphite 50. (Furlong). The mixture is to be freed 
from all moisture by boiling in a steam pot for 2 hours. In 
the hot season of the year it is recommended to add 50 parts 
of burgundy pitch to impart greater hardness to the wax. 

/. Pfanhauser recommends the following composition es- 
pecially for taking moulds from undercut objects. The mass 
is very elastic and objects with quite wide projecting portions 
can, with care, be moulded with it. 

Yellow beeswax 400 parts, ozocerite 300, paraffine 100, 
Venetian turpentine 60, elutriated graphite 100. For use in 
the summer months the composition of the mass is as follows : 
Yellow beeswax 250 parts, ozocerite 450, paraffin 50, Ve- 
netian turpentine 35, elutriated graphite 180. 

The proportions given in the formulas cannot always be 
strictly adhered to and one has to be guided by prevailing 
conditions. If the wax turns out rather brittle, somewhat 



GALVANOPLASTY (REPRODUCTION). 599 

more tallow or turpentine has to be added and, on the other 
hand, in the hot season of the year when the wax is too soft, 
a smaller quantity of turpentine or tallow will have to be 
used. 

To avoid overheating it is advisable not to melt the wax 
mixture over an open fire, and a jacketed kettle heated by 
steam or gas is generally used. With the use of steam, the 
latter passes through a valve into the jacket while the con- 
densed water is discharged through another valve. When 
gas is used the space between the jacket and kettle is filled 
with water, the latter being from time to time replenished as 
evaporation progresses. 

Two wax-melting kettles will be required, because the wax 
which has been in contact with the bath, has to be entirely freed 
from water in the one kettle before it can be again used for 
moulding. The dehydrated wax is then transferred to the 
other kettle. 

To prepare the wax for receiving the impression, pour the 
melted composition in the mould-box, which is a tray of suffi- 
cient size with shallow sides about £ inch in depth ail round, 
and with a continuation of the bottom plate on one of the 
shorter sides for about 3 inches beyond the box, to allow of its 
being supported by hooks from the conducting rods of the 
bath. The moulding-box is placed upon a level surface and 
filled to the brim. Air bubbles and other impurities forming 
on the surface are at once removed by a touch with a hot iron 
rod. 

The surface of the wax, while still luke-warm, is then dusted 
over with the finest plumbago. The black-leaded original is 
then placed, face downwards, upon the wax surface and sub- 
mitted to intense pressure. When black-leading has been 
carefully done, the original can be readily and perfectly de- 
tached from the mould. Some operators apply a light coat of 
oil to the original in place of black-leading it, but care must 
be taken not to leave any considerable portion of oil upon the 
original. 



600 ELECTRO-DEPOSITION OF METALS. 

In this country, before the impression is taken, the wax plate 
or wax mould is frequently treated as follow : Black-lead and 
water are mixed to the consistency of cream. The mixture is 
carefully and uniformly applied to the wax plate and rubbed 
dry with the hand. 

The method above described, according to which the melted 
wax is poured in the moulding-box is constantly more and 
more abandoned, the work being generally done as follows : 

Lead plates, the size of the original to be moulded, are cast, 
laid upon the wax-moulding table, and enclosed by a rim of 
the depth of the required thickness of the wax plate. The 
box thus formed is then filled to the brim with melted wax, 
air-bubbles and other impurities being removed, any excess 
of wax cut off, and the mould black-leaded by means of a soft 
brush. In some galvanoplastic plants the moulded wax plates, 
previous to making the impressions, are planed perfectly level 
by a shaving machine. While gutta-percha matrices will 
bear quite vigorous treatment with the brush, care must in 
this respect be exercised with wax matrices to prevent in- 
jury- 

The wax plates prepared according to the process just 
described are black-leaded and laid upon the originals to be 
moulded, the whole being then placed under the press. 

2. Presses. — For making the impressions of the form in the 
moulding composition, a moulding press is used which is cap- 
able of giving a gradual and powerful pressure. Fig. 141 
represents a form of moulding press in common use, and 
known as the " toggle " press. It consists of a massive frame 
having a planed, movable bed, over which a head is moved 
on pivots and counter-balanced by a heavy weight, as shown, 
so that it can be readily thrown up, having the bed exposed, 
the black-leaded type form being placed on the bed. The 
well black-leaded case is attached b}' clamps to the movable 
head, or the form (also black-leaded) is laid face down on the 
case, and the head is then turned down and held in place by 
the swinging bar (shown turned back in the cut). All being 



GALVANOPLASTY (REPRODUCTION). 



601 



read}', the toggle-pressure is put on by means of the hand- 
wheel and screw, the result being to raise the bed of the press 
with an enormous pressure, causing the face of the type form 
to impress itself into the exposed moulding surface. 



Fig. 141. 




Fig. 142 represents a form of " hydraulic press " less com- 
monly used than that just described. It is provided with 
projecting rails and sliding plate, on which the form and case 
are arranged before being placed in the press. The pump, 
which is worked by hand, is supported by a frame-work on 



602 



ELECTRO-DEPOSITION OF METALS. 



the cistern below the cylinder, and is furnished with a gradu- 
ated adjustable safety-valve to give any desired pressure. 

Metal matrices. — Attempts have for many years been made 
to mould originals in lead, since lead matrices possess many 
advantages over gutta-percha and wax matrices as they do 
not require to be rendered conductive by black-leading, and 
no changes in dimensions take place in consequence of the 
transition from the heated into the cold state. However, 

Fig. 142. 




objects readily liable to injury, such as wood cuts, composi- 
tions, etc., could not withstand the pressure required for im- 
pression in lead plates, and were demolished ; steel plates at 
the utmost were capable of standing the high pressure. 
Serviceable results were not obtained, even with the use of 
very thin lead foil backed, in pressing, with moist paste-board 
or gutta-percha, because the portions of the lead foil subject to 
the most severe demands would tear. 



GALVANOPLASTY (REPRODUCTION). 60S 

To Dr. E. Albert of Munich is due the credit of having dis- 
covered the cause to which these failures were due, and of 
having devised a method for the rational preparation of metal 
matrices. 

Dr. Albert says in reference to this matter * : " Every gal- 
vanoplastic operator knows that in making impressions of 
forms of mixed composition and illustration, tjiat the compo- 
sition down to the quads is impressed before the shades, for 
instance, of a wood cut or an autotype, are finished. In mak- 
ing impressions, the moist paste-board referred to above acted 
exactly in the same manner as wax or gutta-percha softened 
by heating ; i. e. by the moist paste-board the lead foil had to 
be pressed first into the deeper, and finally into the more 
shallow depressions. Notwithstanding the enormous ductility 
of lead, the lead foil could not satisfy these demands on ex- 
tension and, in consequence of this over-demand, tore in many 
places. Hence this process was not available for general 
practice, it being at the utmost suitable only for forms with 
very slight differences in level, and even not for this purpose 
with the large forms now in general use. 

It must be borne in mind that, for instance, upon a square 
millimeter of an autotype there are 36 depressions into which 
the lead foil has to be pressed and to 144 side-walls per square 
millimeter of which it has to attach itself. Especially with 
under-etched printing forms considerable force is required to 
detach the matrix from the moulding material, and it is there- 
fore impossible with larger forms to manipulate the lead foil 
which, for the sake of decreasing the pressure, has to be very 
thin so as to maintain at the same time a level surface. 

This method of impression by which the parts correspond- 
ing to the dark portions of the original can only be impressed 
when the moulding material has been forced into the last cor- 
ner of the deepest depressions of a printing form,*is not pre- 
meditated nor one by choice, but is conditioned on the physical 

* Zur Theorie und Praxis der Metall-matrize, 1905. 



604 ELECTRO-DEPOSITION OF METALS. 

properties of the material itself. The pressure required to force 
the moulding material into the smallest depressions cannot 
be applied so long as the moulding material has a chance to 
escape into an empty space. 

In consequence of this property the matrices have to under- 
go extensive manipulations, since the large angular elevations 
which correspond to the depressions of the printing form would 
prevent the further development of the electro, especially also 
the formation of the copper-deposit upon the matrix. Hence 
the prominent portions have to be removed in the known 
manner. 

' This necessary after-manipulation would of course be im- 
practicable with matrices of thin lead foils, and for this reason 
also the method is not available for line-etching, wood-cut and 
composition. 

In the preceding it has been specified as characteristic of the 
bodies hitherto used for the preparation of matrices that the 
impression of the deepest depressions takes place before that of 
the more shallow ones ; with soft metals, particularly with lead, 
just the reverse is the case. The interior coherence of the 
body-molecules is so much greater in comparison with wax 
and gutta-percha mass, or moistened paste-board, that at the 
commencement of the pressure the lateral escape is avoided, 
whereby the moulding material yields first in the direction ot 
the pressure and fills the smallest depressions. Only with in- 
creasing pressure, which is necessary for forcing the lead into 
the deeper depressions of the printing form, the lead also 
begins to yield laterally in the region of the portions pressed 
first. 

Independent of the fact that the small points already im- 
pressed, which correspond to the smallest impressions of the 
printing form, are again impressed, this pushing of the lead 
has the furlher drawback that the lead firmly settles in these 
smallest depressions, thus rendering the original useless. 

Besides, there is no type composition, no wood-cut, etc., the 
printing elements of which, especially when standing isolated, 



GALVANOPLASTY (REPRODUCTION). 605 

could withstand the enormous pressure which has to be used 
for forcing a lead plate at least 5 millimeters thick into the 
large depressions. However, such a thickness of the lead 
plate would be necessary just as with wax and gutta-percha 
impressions, since the difference in height between printing 
and justifying surface is about 1 cieero = 4.5 millimeters. 

Hence, with the means hitherto available, the production of 
matrices, either with thin or thick metal plates, was imprac- 
ticable, and until lately recourse had to be had to the old and 
qualitatively inferior wax and gutta-percha matrices, till Dr. 
Albert, in 1903, succeeded in finding a method for the rational 
production of metal matrices. 

This method is based upon a number of inventions patented 
in all civilized countries, and the characteristic features of the 
process will here be briefly given. 

The basis for the solution of the problem rested upon the 
adoption of such a thickness of the metal plate, that the man- 
ipulations required for the production of the matrix and its 
after-manipulations without deformation could be effected by 
the hand of any workman ; as well as upon a new method of 
impressing which would render it possible for the thickness of 
the plate to be materially less than the relief difference of the 
printing form. 

While in the production of medals and coins by means of 
galvanoplasty, the problem consists in a perfectly detached 
reproduction of all the differences- in level of the original, with 
an electro for graphic purposes, the impression of the matrix 
in the large depressions is only a matter of technical necessity 
so that in the subsequent use of the electro for printing the 
white portion will not smear. This knowledge led to the ex- 
pedient of pressing or bending by means of a support of a soft 
body, the about 2 millimeters thick lead plates only so far 
into the above-mentioned depressions as required for technical 
reasons. 

Hence this method of impression is based upon a combina- 
tion of pressing and bending. The lead is bent to a greater 



606 



ELECTRO-DEPOSITION OF METALS. 



extent the larger and wider the sunk surface is, the electro 
automatically receiving thereby all the white portions of such 
depth that they do not smear in printing. 

The process may be explained by Figs. 143 and 144. 

Fig. 143 represents the arrangement of the platen, lead 
plate, and soft intermediate layer previous to the moment of 
impression. The material used for the intermediate layer 
must possess certain properties and must be softer than the 
moulding material. It should be compressible without materi- 
ally yielding laterally under pressure and, by reason of elas- 
ticity or internal friction, also oppose a certain resistance to 
compression in order to bend with this resisting power of the 
lead-plate where the latter lies hollow. On the other hand, it 

Fig. 143. 





must not be too soft in the sense of its affinity to a liquid 
aggregate state, as, for instance, heated wax, but it should be 
more porously soft either in conformity with its nature or its 
arrangement. In principle the latter is generally based upon 
the production of many empty intermediate spaces in the 
material (wood shavings and snow are softer than wood and 
ice), or upon placing many thin layers of the material one 
above the other. Such bodies can be compressed without 
yielding too much laterally. If the character of the body 
approaches more the liquid state, more elastic properties have 
to be added, which by their tendency to equalize the change 
suffered in form counteract the lateral yielding, or other 
checks have to be arranged. Besides, a certain degree of 



GALVANOPLASTY (REPRODUCTION). 



607 



elasticity is useful for bending the lead plate on the free-lying 
places. 

Such an intermediate layer may appropriately consist of a 
number of layers of paper. Such a layer, by reason of the 
character of the paper fiber itself, as well as of the intermediate 
layer of air, is soft and elastic as regards the direction vertical 
to the impression-plane, while on the other hand the texture 
of the paper-stuff affords the necessary checks in the direction 
parallel to the impression-plane to prevent, after the com- 
mencement of pressure, the lateral yielding of the interme- 
diate layer. The latter important property was in former 
experiments neutralized by moistening the paper. 

In Fig. 144 the platen has sunk so that the intermediate 

Fig. 144. 




layer opposite to the places o o' ', from which the first counter, 
pressure emanates, is compressed to one-half of its original 
volume. At the moment when the intermediate layer has by 
compression acquired the degree of hardness of the moulding 
material, it is forced by the next increase in pressure into the 
small depressions of the plane o o' . On the places opposite to 
u u f , the lead, which lies here perfectly free, and hence exerts 
no counter-pressure, is at the same time pressed into the hol- 
low space u u' by the resisting force of the intermediate layer. 
The same is also the case opposite to the places m m' , but 
the bending takes place in a less degree, just as a board rest- 
ing upon supports 6 feet apart is more bent by a weight than 
one whose supports are only 3 feet apart. 



608 ELECTRO-DEPOSITION OF METALS. 

This also answers technical requirements, since the white 
portions smear the more readily in the press, the greater their 
dimensions are. 

Thus there had always been made the gross error of treating 
according to the same principles which had proved good for 
wax and gutta-percha, a body, such as lead, of an entirely 
different physical character. The process of pressing had in 
the main to be excluded, and a bending process substituted 
for it. This was rendered possible by a suitable thickness of 
the moulding material, and by backing it with a soft and 
yielding body, which, as regards its extensibility parallel to 
the impression-plane, was checked by its texture or otherwise. 

By this bending process the pressure required for impres- 
sion was under certain circumstances reduced to one-tenth of 
its former magnitude, so that metal matrices could also be 
produced from wood-cuts and composition. 

This reduction in pressure is least manifest with printing 
forms with many very fine and crowded printing elements, for 
instance, autotypes, for which, according to the character of 
the picture, a pressure of 500 to 1000 kilogrammes per square 
centimeter is required ; this is more than hitherto used for 
wax and gutta-percha. 

The problem of the production of metal matrices was thus 
solved only for forms of moderate size, since, although the 
pressure had been largely reduced by the selection of a correct 
thickness of the lead plate and by backing the latter with a 
soft, elastic body, it was nevertheless much greater than that 
required for wax and gutta-percha. The ordinary hydraulic 
presses, with some few hundred atmospheres, were therefore 
not available for impressing larger forms. 

By the use of successive partial pressure with the simultan- 
eous introduction of side-pressure, Dr. Albert has succeeded in 
increasing, at a small expense, about twenty times the 
capacity of every press now in use. 

The gradual progression of a limited pressure over the 
entire printing form also prevents the extremely troublesome 



GALVANOPLASTY (REPRODUCTION). 609 

phenomena appearing in other methods of impressing, namely, 
that it is impossible for the process of impression being affected 
by occluded air, the latter having at any time a chance to 
escape. 

The impressions being automatically effected, there is no 
loss of time worth speaking of with this method. Thus, for 
instance, only 55 seconds were required for impressing a form 
of the "Woche," and not quite two minutes for one of the 
" Berliner Illustrierte Zeitung." For impressing illustration- 
forms of the same size without letters, only half the above- 
mentioned time was necessary. 

Thus there is no difficulty whatever in executing impres- 
sions of any size. 

Fischer endeavors to attain the same object as Dr. Albert by 
the use of lead plates with corrugated backs, small pyramids 

j AAA Aj aD0U t 2 to 3 millimeters high being thus formed. 

These corrugations act like Albert's elastic intermediate layer 
in so far that the lead plates are not pressed, but bent, into 
the deep portions of the printing form, a reduction in the 
otherwise high pressure required being thus effected. Now, 
suppose in Fig. 144, instead of an elastic intermediate layer, 
a lead plate with corrugated back is placed upon the form, 
the small pyramids which are opposite to the portion o o' of 
the printing form are first compressed, while the part of the 
lead plate corresponding to the portion u u' is bent through 
by the pressure exerted .by the platen upon the points of the 
corrugations, the latter being thereby not very much flattened. 
If now the pressure be increased the lead plate is first flattened 
at o o' , and then the actual impression, i. e., pressing the lead 
into the design of the original or into the composition begins. 
Kunze does not use corrugated lead plates, but provides the 
platen with corrugations, and combines therewith a process of 
successive partial pressure invented by him. (German patent 
applied for.) As the patent has not yet been granted, details 
of the process cannot be given. 
39 



610 ELECTRO-DEPOSITION OF METALS. 

3. Further manipulation of the moulds. — The moulds when 
detached from the original show in addition to the actual 
impression certain inequalities which have to be removed. 

With gutta-percha moulds such inequalities in the shape of 
elevations, are carefully pared away with a sharp knife, while 
with wax moulds they are melted down. For this purpose 
serves a brass tube about 4 inches long, drawn out to a fine 
point and connected by means of a rubber tube with a gas 
jet. By opening the gas-cock more or less, the gas burns with 
a larger or smaller pointed flame, and the brass tube is guided 
by the hand, so that the elevations are melted down and the 
deeper portions of the electrotype will present a smooth ap- 
pearance. A more modern instrument for this purpose is so 
arranged that the flame can be regulated by the finger pres- 
sing upon a rubber bulb. However, not only the inequalities 
are melted down, but the upper edges, of the steep contours of 
the impression are melted together, and melted wax is built 
up all around in order to enlarge the depressions in the elec- 
trotype and avoid cutting. The wax is readily built up by 
holding in one hand a thin stick of wax at a distance of about 
0.19 inch from the edge of the impression and at about the 
same distance above the mould, and melting off the wax, 
drop by drop, b} 7 means of a pointed flame guided by the 
other hand. One drop is placed close alongside the other, and 
when the entire edge of wax is thus completed it is made 
perfectly smooth by again melting with the pointed flame. 

The next process is 

4. Making the moulds conductive, without which a galvano- 
plastic deposit would be impossible. Black-lead is almost 
exclusively used for this purpose, and must be of the purest 
quality and in a most minute state of division. The best 
material for this purpose is prepared from the purest selected 
Ceylon graphite, which is ground by rolling with heavy iron 
balls until it is reduced to a dead black, impalpable powder. 

Black-leading the moulds is performed either by hand or 
more commonly by machines. 



GALVANOPLASTY (REPRODUCTION). 



611 



Fig. 145 shows one of these machines with its cover re- 
moved to exhibit its construction. It has a traveling carriage 
holding one or more forms, which passes backward and for- 
ward, under a laterally vibrating brush. Beneath the machine 



Fig. 145. 




is placed an apron which catches the powder, which is again 
used. 

Another construction of a black-leading machine is shown 
in Fig. 146, the details of which will be understood without 
lengthy description. The moulds are placed upon the slowly 
revolving, horizontal wheel, upon which the brush moves 
rapidly up and down with a vertical, and at the same time 



612 



ELECTRO-DEPOSITION OF METALS. 



lateral, vibrating motion. The black-leading space being 
closed air-tight, scattering of black-lead dust is entirely pre- 
vented, the excess of black-lead collecting in a vessel placed 
in the pedestal. 

On account of the dirt and dust caused by the dry process 
of black-leading, some electrot}^pers prefer the wet process 
as it is claimed to work more quickly and neatly, producing 
moulds that are thinly, evenly and perfectly covered. The 

Fig. 146. 




moulds are placed upon a shelf in a suitable receptacle, and a 
rotary pump forces an emulsion of graphite and water over 
their surface through a traveling fine rose-nozzle. 

Black-leading machines have recently been introduced, their 
action being based upon the principle of the blast. The graph- 
ite powder is by means of a current of strongly-compressed 
air carried with considerable force towards the surface of the 
mould to be black-leaded. The process of making the moulds 



GALVANOPLASTY (REPRODUCTION). 613 

■conductive according to this system, is claimed to be thorough 
and complete and quickly accomplished. However, many 
operators prefer black-leading by hand, especially moulds of 
autotypes, the lines remaining sharper. 

5. Electrical contact. — The black-leaded moulds have now to 
be provided with contrivances for conducting the current upon 
the black-leaded surface. 

With gutta-percha moulds, the edges are trimmed off to 
within 0.19 to 0.31 inch of the impression. In two places on 
the edges of the mould holes are made by means of an awl. 
Through these holes stout copper wires doubled together are 
drawn, so that after twisting them together they lie firmly on 
the edge of the mould. These wires serve for suspending the 
mould to the conducting rod, and previous to twisting them 
together, two fine copper wires, the so-called feelers, are placed 
between them and the edge of the mould. The object of these 
thin wires being to effect the conduction of the current to the 
lower portions of the mould, they must be firmly secured in 
twisting together the suspension-wires. 

However, before allowing these feelers to rest upon the 
black-leaded surface, the place of contact of the wire with the 
mould is again thoroughly brushed with black-lead, in order 
to be sure that the current will not meet with resistance on 
these points. With very large moulds it is advisable to use 
more than two feelers and to arrange them especially in 
deeper depressions. The thickness of the feelers should be 
about that of horse-hair. 

No black-lead should get on the edges or back of the mould, 
otherwise copper would also be deposited on them. 

In place of the wires for suspending the mould, the method 
for wax moulds described below may also be applied, a small, 
hot copperplate being melted in on the edge of the mould and 
the latter secured to the conducting rod by means of a hook. 

Gutta-percha moulds, being specifically lighter than the 
copper bath, would float in it, and have, therefore, to be 
loaded by securing heated pieces of lead to the backs. 



614 



ELECTRO-DEPOSITION OF METALS. 



Fig. 147. 



For black-leaded wax moulds the process is as follows : A 
bright copper plate about 1.18 inches square and 0.039 inch 
thick is melted in on the upper edge of the mould, and the 
edges are leveled by means of a pointed flame, so as to pro- 
duce a smooth joint between the copper plate and wax surface. 
This place is again thoroughly black-leaded with the hand, and 
the edges, having been first beveled, are then melted together 
with the flame. The wax over the hole in the lead plate 
through which the hook of the mould-holder is pushed is 
finally removed with a knife. The shape of the mould- 
holder is shown in the accompanying illustration, Fig. 147. 
The hook to which the mould is suspended is insulated from 
the rest of the holder by hard rubber plates, and the screw- 
threads by hard rubber boxes, so that the 
lead plate which comes in contact with the 
hook receives no current, and no copper can 
deposit upon it. The small, square block 
cast on the holder lies perfectly level upon 
the copper plate in the mould, a good and 
abundant conduction of current being thus 
effected, such as is absolutely required, for 
instance, for rapid galvanoplasty. 

To prevent the copper deposit from spread- 
ing much beyond the impression towards the 
edge, it has been proposed to cover these 
portions of the mould with strips of glass, 
hard rubber, or celluloid. For this purpose 
heated glass strips, 0.15 inch wide and 0.19 
inch high, are pressed about 0.079 inch deep into the wax 
mould so as to form a closed frame around the impression. 
Strips of hard rubber or celluloid of the above-mentioned 
width and height, are fastened together with copper pins. 
By these means the object in view is perfectly attained. 

With very deep forms of type, it is sometimes of advantage 
to first coat the black-leaded surface with copper, in order to 
obtain a uniform deposit in the bath. The process is as fol- 




GALVANOPLASTY (REPRODUCTION). 615 

lows : Pour alcohol over the black-leaded form, let it run off, 
and then place the form horizontally over a water trough. 
Now pour over the form blue vitriol solution of 15° to 16° Be., 
dust upon it from a pepper-box some impalpable fine iron 
filings and brush the mixture over the whole surface, which 
thus becomes coated with a thin, bright, adherent film of 
copper. Should any portion of the surface after such treat- 
ment remain uncoppered, the operation is repeated. The ex- 
cess of copper is washed off and the form, after being provided 
with the necessary conducting wires, is ready for the bath. 

Gilt or silvered black-lead is also sometimes used for very 
deep forms. It is, however, cheaper to mix the black-lead 
with £ its weight of finest white bronze powder from finely 
divided tin. When forms thus black-leaded are brought into 
the copper bath, the particles of tin become coated with 
copper, also causing a deposit upon the black-lead particles in 
contact with them. 

6. Suspending the mould in the bath. Previous to suspend- 
ing the mould in the copper bath, it has to be perfectly freed 
from every particle of black lead which might give rise to 
defects in the deposit. 

Strong alcohol is then poured over the mould, the object of 
this being to remove any traces of greasy impurities, which are 
readily dissolved and removed by the alcohol. Moulds thus 
treated at once become uniformly wet in the bath, which, if 
this precaution be omitted, is not the case, and causes an 
irregular formation of the deposit (by air-bubbles). 

The moulds are suspended in the bath in the manner above 
described, special attention being paid to having them hang 
parallel to the anodes so that all portions of them may receive 
a uniform deposit. 

Before being suspended in the bath, the backs of lead mat- 
rices should be provided with a protecting layer of celluloid or 
other suitable material to prevent them from becoming cop- 
pered. 

7. Detaching the deposit or shell from the mould, a. From 



616 



ELECTRO-DEPOSITION OF METALS. 



gutta-percha moulds. When the mould has acquired a deposit 
of sufficient thickness, it is taken from the bath, rinsed in water, 
and all edges which might impede the detachment of the de- 
posit from the mould are removed with a knife. The deposit 
is then gradually lifted by inserting under one corner a flat 
horn plate, or a thin dull brass blade, and applying a very 
moderate pressure. Particles of gutta-percha which may still 
adhere to the deposit, are carefully burnt off over a flame, 
b. From wax moulds. Wax moulds are placed level upon 

Fig. 148. 




a table, and hot water is several times poured over them. By 
pushing the finger-nail under one corner of the deposit, it can 
readily and without bending be detached from the softened 
wax. If not successful at first, continue pouring hot water 
over the mould until the deposit can be detached without 
difficulty. 

In larger establishments, a cast-iron moulding and melting 
table, such as is shown in Fig. 148, is used for wax moulds. 
The planed table plate is hollow, and by means of tongues 



GALVANOPLASTY (REPRODUCTION). 617 

cast to the plate the steam which is introduced is forced to 
uniformly heat the entire plate. The electrotypes are placed 
upon the plate, the wax side down. The wax melts and runs 
through stop-cocks on the side into a jacketed copper kettle, 
which can be heated by steam for melting the wax. The iron 
ledges screwed upon the table plate are made tight with as- 
bestos paper, so that the wax cannot run off except through 
the stop-cocks. 

If the table is to be used for moulding the wax plates, cold 
water, instead of steam, is allowed to circulate through the 
hollow table plate, whereby rapid congealing of the wax is 
effected. 

Two such kettles are required, since the wax which has been 
in contact with the bath has to be for several hours heated in 
one of the kettles to render it free from water before it can be 
again used for moulding. The wax freed from water is brought 
into the kettle and used for moulding wax plates. 

c. From metal-matrices. If the matrix has been free from 
fat, the deposit adheres ver}^ firmly, and cannot be lifted off 
in the ordinary manner as with gutta-percha matrices ; nor 
can the deposit be separated from the lead by melting the 
latter, as with the temperature required for this purpose, the 
copper shell might be damaged. 

Albert found that by allowing the metal matrix together 
with the copper deposit to float upon readily fusible metallic 
alloys with many free calories, the deposit, in consequence of 
the unequal expansion of the metals, can completely and 
without injury be separated. By detaching the deposit in 
this manner, Albert succeeded in using the lead matrix freed 
from the deposit four times for the preparation of electros, the 
last electro thus made being not inferior in quality to the 
first one.* 

8. Backing the deposit or shell. The face of the electro is 
first freed from all residues by careful burning off over a flame 

*Dr. E. Albert, " Zur Theorie und Praxis der Metall-Matrize," p. 10. 



618 ELECTRO-DEPOSITION OF METALS. 

and washing with benzine, and scoured bright with whiting 
and hydrochloric acid. The edges are then trimmed with 
shears to the width of a finger from the picture. The tinning 
of the back of the shell is the next operation, and has for its 
object the strengthening of the union between the shell and 
the backing metal. For this purpose the back of the shell is 
cleansed by brushing with " soldering fluid," made by allow- 
ing hydrochloric acid to take up as much zinc as it will dis- 
solve, and diluting with about one-third of water, to which 
some ammonium chloride is sometimes added. Then the 
shell, face down, is heated by laying it upon an iron soldering 
plate, floated upon a bath of melted stereotype metal, and, 
when hot enough, melted solder (half lead and half tin) is 
poured over the back, which gives it a clean, bright metallic 
covering. Or the shell is placed downward in the backing- 
pan, brushed over the back with the soldering fluid, alloyed 
tinfoil spread over it, and the pan floated on the hot backing 
metal until the foil melts and completely covers the shell. 
When the foil is melted the backing-pan is swung on to a 
leveling stand, and the melted backing metal is carefully 
poured on the back of the shell from an iron ladle, commenc- 
ing at one of the corners and gradually running over the sur- 
face until it is covered with a backing of sufficient thickness. 
Another method is as follows : After tinning the shell it is 
allowed to take the temperature of the backing metal on the 
floating iron plate. The plate is then removed from the melted 
metal, supported in a level position on a table having project- 
ing iron pins, on which it is rested, and the melted stereotype 
metal is carefully ladled to the proper thickness on the back 
of the tinned shell. This process is called "backing." The 
thickness of the metal backing is about an eighth of an inch. 
A good composition for backing metal consists of lead 90 parts, 
tin 5 and antimony 5. An alloy of lead 100 parts, tin 3 and 
and antimony 4 is also recommended as very suitable. 

9. Finishing. — For this purpose the plates go first to the saw 
table (Fig. 149) for the removal of the rough edges by means 



GALVANOPLASTY (kEPRODUCTION). 



619 



of a circular saw. The plates are then shaved to take off any 
roughness from the back and make them of even thickness. 
In large establishments this portion of the work, which is very 
laborious, is done with a power planing or shaving machine, 
types of which are shown in Figs. 150 and 151, Fig. 150 being 
a shaving machine with steam one way, and Fig. 151 one 
with steam both ways. By means of a straight-edge, the 

Fig. 149. 




plates are then tested as to their being level, and any un- 
eveness is rectified by gentle blows with a polished hammer, 
care being taken not to damage the face. The plate then 
passes to the hand-shaving machine, where the back is shaved 
down to the proper thickness, smooth and level. The edges 
of the plate are then planed down square and to a proper 
size, and finally the plates are mounted on wood type-high. 



620 ELECTKO-DEPOSITION OF METALS. 

Book-work is generally not mounted on wood, the plates 
being left unmounted and finished with beveled edges, by 
which they are secured on suitable plate-blocks of wood or 
iron supplied with gripping pieces, which hold them firmly 
at the proper height, and enable them to be properly locked up. 

Fig. 150. 




Copper deposits from metallic surfaces. — It remains to say a 
few w r ords about the process, by which a copy may be directly 
made from a metallic surface without the interposition of wax 
or gutta-percha. If the metallic surface to be moulded were 
free from grease and oxide, the deposit would adhere so firmly 
as to render its separation without injury almost impossible. 



GALVANOPLASTY (REPRODUCTION). 



621 



Hence, the metallic original must first undergo special prepa- 
ration, so as to bring it into a condition favorable to the detach- 
ment of the deposit. This is done by thoroughly rubbing the 
original with an oily rag, or, still better, by lightly silvering it 
and exposing the silvering for a few minutes to an atmosphere 
of sulphuretted hydrogen, whereby silver sulphide is formed, 
which is a good conductor, but prevents the adherence of the 
deposit to the original. For the purpose of silvering, free the 

Fig. 151. 




surface of the metallic original (of brass, copper, or bronze) 
from grease, and pickle it by washing with dilute potassium 
cyanide solution (1 part potassium cyanide to 20 water). 
Then brush it over with a solution of 4J drachms of silver 
nitrate and 1 oz. 6 drachms of potassium cyanide (98 per cent.) 
in one quart of water ; or, still better, immerse the original for 
a few seconds in this bath, until the surface is uniformly coated 
with a film of silver. The production of the layer of silver sul- 



622 ELECTRO-DEPOSITION OF METALS. 

phide is effected according to the process described later on. 
The negative thus obtained is also silvered, made black with 
sulphuretted hydrogen, and a deposit of copper is then made, 
which represents an exact copy of the original. Instead of 
sulphurizing the silvering with sulphuretted hydrogen, it may 
also be iodized by washing with dilute solution of iodine in 
alcohol. The washed plate, prior to bringing it into the 
copper bath, is for some time exposed to the light. 

To prevent the reduction of copper on the back of the 
metallic original to be copied, it is coated with asphalt lacquer, 
which must be thoroughly dry before bringing into the bath. 
When the deposit of copper is of sufficient thickness, the plate 
is taken from the bath, rinsed in water, and dried. The edges 
are then trimmed off by filing or cutting to facilitate the sepa- 
ration of the shell from the original. 

Of course only metals which are not attacked by the acid 
copper solution can be directly brought into the bath. Steel 
plates must therefore first be thickly coppered in the alkaline 
copper bath, and even this precaution does not always protect 
them from corrosion. It is therefore better to produce in a 
silver bath (formula I., p. 368) a copy in silver of sufficient 
thickness to allow of the separation of both plates. The silver 
plate is iodized, and from it a copy in copper is made by the 
galvanoplastic process. The copper plate thus obtained is an 
exact copy of the original, and after previous silvering, the 
desired number of copies may be made from it. 

Other operations which may have to be done in galvano- 
plastic plants, for instance, coppering of zinc etchings, and of 
stereotypes, and nickeling and cobalting the latter, as well as 
electrotypes, have already been described in the part devoted 
to electro-plating, so that few words will here suffice. 

Stereotypes are, as a rule, coppered in the acid copper bath, 
stereotype metal being not attacked by it. The bath, how- 
ever, should not have a large content of free sulphuric acid. 
In order to have the copper adhere well the plates, previous 
to being brought into the bath must, of course, be thorough!}' 



GALVANOPLASTY (REPRODUCTION). 623 

freed from grease by brushing with warm soda solution and 
whiting. 

Zinc plates are thoroughly freed from grease, and then cop- 
pered or brassed. Nickeling is effected according to the pro- 
cess given under " Deposition of Nickel." 

Preparation of type-matrices. — The process varies according 
to whether the originals consist of zinc or of a material (lead- 
antimony-bismuth alloy) indifferent towards the acid copper 
bath. 

It is best to brass zinc originals, and to give the brass de- 
posit higher lustre by polishing with Vienna lime powder 
upon a small flannel bob. They are then freed from grease 
by brushing with quicklime, silvered by the method previously 
given, and iodized. The surfaces which are to remain free 
from deposit are stopped off with wax, and the originals 
placed in the acid copper bath, care being taken to bring 
them in contact with the current-carrying conducting rod be- 
fore immersion in the bath. 

Originals of hard lead or similar alloys, after having been 
suitably prepared, may be directly suspended in the copper 
bath, since a heavy copper deposit can be quite readily de- 
tached from them, though slightly oiling them will do no 
harm. 

The current-density for depositing must be slight to prevent 
formation of buds. The deposit is generally made 0.079 to 
0.098 inch thick, when it is detached from the original, and 
after filing the edges backed with zinc or brass. The matrix 
is finally justified. 

Regarding nickel matrices, see " Galvanoplasty in Nickel." 

Electro-etching. — It is in place here to discuss the process of 
electro-etching, it being chiefly applied in the graphic indus- 
tries, and a few methods of etching, which are not executed 
by electrical means, will first be referred to. 

Methods of dissolving the various metals by acids were 
probably known many centuries ago, it being beyond doubt 
shown by the notable productions of the goldsmiths, as well as 



624 ELECTRO-DEPOSITION OF METALS. 

of the armorers, about the year 1400, that they possessed a 
knowledge of etching. It may also be supposed that the 
niello work of the goldsmiths was the forerunner of copper 
engraving, an art still highly appreciated at the present day, 
and the earliest impression of which dates from the year 1446. 

There are four different methods of copper engraving, but 
that in which etching plays an important role, would seem to 
be the most interesting. 

To protect separate portions of metallic surfaces from the 
action of the acid, a so-called covering or etching ground is 
used, which consists of a mixture of 2 \ parts asphalt, 2 parts 
wax, 1 paft rosin and 2 parts black pitch, applied hot. 

The copper engraver uses for his work another composition 
of resins, and it is here given because this covering ground has 
proved capable of resisting 25 per cent, nitric acid. Yellow 
wax 4 parts, Syrian asphalt 4, black pitch 1, and white Bur- 
gundy pitch 1. Melt the ingredients, and when the mixture 
boils, gradually add, whilst stirring constant!}', 4 parts more 
of pulverized Syrian asphalt. Continue boiling until a sample 
poured upon a stone and allowed to cool breaks in bending. 
Then pour the mixture into cold water and shape it into small 
balls, which for use are dissolved in oil of turpentine. 

Upon a heated plate, ground perfectly level, the copper en- 
graver then applies the above-mentioned covering ground so 
thin that the metallic surface appears golden-yellow. The 
covering ground is next blackened by means of a wax torch, 
and the outlines of the picture to be made are then sketched. 

Now commences the work which shows the artistic talent of 
the engraver. With a fine etching-needle he scratches the 
contours of the picture into the covering ground, without, 
however, injuring the metal, and finishes his work by nar- 
rower and wider lines until the desired effect is believed to be 
produced. 

However, to make this work fit to be printed, the lines of 
the picture must lie depressed in the metal plate. For this 
purpose the plate is surrounded with a wax rim and subjected 



GALVANOPLASTY (REPRODUCTION). 025 

to etching with nitric acid or, more recently, with ferric chlo- 
ride. After the at first weak acid has acted for a short time, 
the finest lines have acquired the required depth. The fluid 
is then poured off and the fine lines are stopped off, when 
etching is recommenced. Thus progressing, a picture with 
lines becoming constantly deeper, as well as broader, is formed, 
the result finally showing the artistic talent of the engraver. 
The plate is cleansed and handed to the printer, or it may be 
steeled or manifolded by galvanoplasty. 

While speaking of this process of copper-engraving, our at- 
tention is involuntarily directed to a very interesting achieve- 
ment, which deserves mention in connection with the work of 
the etcher and of the operator in galvanoplasty. The process is 

Photo-engraving, by means of which copper plates, as well as 
small and also very extensive pictures, of such high artistic 
value can be produced that they form at present an important 
branch of the art business. 

Former investigators have shown : 

1. That of all the varieties of glue, gelatine possesses the 
greatest swelling capacity. 

2. That when mixed with potassium dichromate and ex- 
posed to the action of light, gelatine becomes insoluble, i. e., 
it loses entirely its power of swelling. 

Upon this is based the following process : Take a sheet of 
well-sized paper and make a rim around it, about 0.39 inch 
high, by turning up the sides. The paper thus prepared, 
which now forms a sort of dish, is placed upon a perfectly 
level surface and a solution, consisting mostly of gelatine col- 
ored black, is poured over it. Such paper is found in com- 
merce under the name of black pigment paper. It is immersed 
in solution of ammonium dichromate, dried in a dark room 
and stored for use. 

A perfect diapositive of the original is placed in a copying 
frame and, after covering it with the prepared pigment paper, 
the frame is closed. 

By the rays of light which strike the prepared paper through 
40 



626 ELECTRO-DEPOSITION OF METALS. 

the diapositive, the layer of chromium and gelatine is hard- 
ened, the process taking place in the same gradations of tone 
as conditioned by the diapositive. After sufficient exposure to 
the light, the pigment paper is placed in a water bath and a 
quite perceptible picture in relief will in a short time appear. 
The portions which had not been exposed to the light, swell 
up very much and lose the greater part of the coloring matter 
mixed with the gelatine. The result is, therefore, the reverse 
of the diapositive used. 

By means of an ingenious contrivance, a layer of impalpable 
asphalt powder has in the meanwhile been applied to a finely 
ground copper-plate, and melted upon it. The above-men- 
tioned chrome-gelatine picture is now placed upon the plate 
and is made to adhere by rubbing. The paper can now be 
readily detached, while the picture adheres to the copper- 
plate. The gelatine-layer forms the protection from the effect 
of the etching with ferric chloride. 

It will be readily understood that for this, and all the pre- 
ceding manipulations, great skill and years of experience are 
required in order to produce such results as we have occasion 
to admire in the art stores. 

If galvanoplasty is to be employed for the production of 
such copper-plates, a glass or metal plate is used and coated 
with the chrome-gelatine above described. It is then exposed 
to the light under a photographic glass negative, allowed to 
swell up, and for a short time laid in a weak chrome alum 
solution. The layer is then so hard as to allow of making a 
wax mould and an electrotype. The process is called photo- 
galvanography. 

The swelling power of gelatine, as well as its insolubility, 
has led to the production of collographic printing. The man- 
ipulations for the preparation of the printing plates required 
for this purpose differ but little from those for photo-galvan- 
ography. 

Pour over a glass plate, 0.19 to 0.27 inch thick, a layer of 
chrome-gelatine, which, however, must not be colored, and 



GALVANOPLASTY (REPRODUCTION). 627 

place the plate in a drying-oven heated to 113° F. The plate 
is then exposed to the light under a photographic negative 
and the layer of gelatine allowed to swell up. 

Another property shown by chrome-gelatine is that the 
portions which have become insoluble by exposure to light 
are very susceptible to fat colors. If now such a glass plate 
be wiped over wdth a moist sponge and then blackened all 
over by means of a suitable color with the use of a roller, a 
picture showing all the details of the negative used appears 
upon the glass plate. By placing upon this picture a sheet 
of printing-paper, and drawing both through the collographic 
printing-press, the color adheres to the paper. 

An etching process which includes all the improvements 
made in metal etching, and which, by reason of the great 
progress made in photography, has won a great field of activ- 
ity, is 

Zincography.— All plates produced by this process are in- 
tended for book printing, and must show all the lines and 
points of the picture in relief, while the parts which in print- 
ing result in the white portions of the picture should be as 
deep as possible. It is obvious that this requirement makes 
the highest demands on the etching process, and that long 
experience and perseverance are required to achieve excel- 
lency in this respect. 

All former experiments will here be omitted, and only the 
process which has proved of practical value will be described. 

Freshly-made impressions are reprinted upon fine zinc 
plates ground perfectly level, drawings executed with suitable 
ink upon prepared paper being used in the same manner. 

When the reprints have been successfully made and any 
defects removed by retouching, very finely powdered rosin is 
poured upon the metal plate and rubbed with a brush into 
the points and lines of the drawing. Since no rosin powder 
adheres to the portions of the plate not printed on, the plate 
may at once be laid upon the hot-plate and highly heated. 
The rosin powder combines intimately with the printing ink, 
a layer which well resists weak nitric acid being thus formed. 



628 ELECTRO-DEPOSITION OF METALS. 

After etching for a short time with dilute nitric acid, fine 
silvery edges produced by the washing away of the dissolved 
metal appear on all the lines and points of the reprint. If 
etching would now be continued, the lines and points would 
also be laterally attacked by the acid. Over-etching would 
thus take place, and all the fine portions of the picture disap- 
pear. Hence a fresh protecting cover has to be applied, which 
protects from corrosion, not only the surfaces of the lines and 
points, but also the above-mentioned silvery edges. For this 
purpose, the etcher uses a lithographic roller and a suitable 
etching color. The drawing is then dusted over, and the 
plate heated as previous to the first etching. Proceeding in 
the same manner, the manipulations are repeated until the 
plate has the necessary depth for printing. Finally, all un- 
necessary metal is cut away with a fret-saw, and the etching 
having been mounted on wood, is ready to be given to the 
printer. 

If, however, the original handed in for reproduction, is to 
be enlarged or reduced, a photographic negative of it is first 
made and copied directly upon the zinc plate. For this pur- 
pose, a coating of asphalt solution, or of a mixture of egg or 
glue with ammonium dichromate, is applied to the zinc plate, 
and the negative having been placed upon the latter, it is ex- 
posed to the light. The result is the same as has been de- 
scribed under photo-engraving, a picture being obtained which 
is exactly treated as the reprinted drawings, i. <?., powdered, 
heated, and etched. 

Another process of transferring is effected by reprinting : 

A sheet of paper coated with chrome-gelatine is dried in a 
dark room, placed in a copying frame under a negative and 
exposed to the light until a beautiful, chestnut-brown picture 
is perceptible. The chromium salt is dissolved in the water 
bath, the picture inked with reprinting ink and, after drying, 
transferred to the metal plate. 

Up till now we have only spoken of points and lines, be- 
cause the originals have to be composed of such to be suitable 



GALVANOPLASTY (REPRODUCTION). 629 

for the reproduction process. Photography, however, makes 
it also possible to transform water-color paintings, photo- 
graphs, India-ink sketches, etc., into book-printing plates. 

For this purpose the photographer uses a glass plate pro- 
vided with a network of very fine lines, places it between the 
sensitive glass plate and the original, and thus produces a neg- 
ative, which, though composed of millions of small points, 
nevertheless gives all the shadings of the original. This pro- 
cess is called autotypy, and is at present used to such an extent 
and has been brought to such a state of perfection, as to make 
it difficult to say when the limit of what can be done by the 
etching process in connection with photography may be 
reached. 

The achievements in photography widen almost daily the 
field of activity of the etcher, and it may be anticipated that 
printing plates will in this manner be produced which, when 
printed in three colors, will yield impressions such as could 
formerly only be attained by the lithographer with the use of 
many stones. It is by no means impossible that the electric 
current may before long be utilized in the execution of the 
above-mentioned etching processes, and for this reason a few 
hints will here be given which may be of use to the galvano- 
plastic operator. 

In etching steel, copper or zinc plates, in the ordinary way, 
a covering ground, as previously mentioned, is applied to the 
plate to be etched. The drawing is then transferred to the 
covering ground and traced with the graver, taking care ihat 
the tool lays bare the metal in all the lines. A rim of wax is 
then made around the plate, and dilute nitric acid or another 
solution poured over it. The basis-metal is attacked by the 
acid and the drawing is thus etched. 

The injurious acid vapors evolved thereby and the lateral 
corrosion of the lines, as well as other drawbacks, have brought 
about the execution of etching with the assistance of the elec- 
tric current, the above-mentioned drawbacks being thereby 
obviated, and more rapid and reliable working rendered pos- 



630 ELECTRO-DEPOSITION OF METALS. 

sible. The plate is treated in exactly the same manner as for 
ordinary etching, but instead of furnishing it with a wax rim 
and pouring acid over it, it is suspended in a suitable solution 
as anode — hence connected with the positive pole — a metal 
plate of the same size connected with the negative pole being 
suspended parallel to it. The metal is dissolved by the acid- 
residue appearing on the positive pole. 

For copper-plates which are to be etched, the ordinary acid 
copper bath is used ; for zinc-plates, solution of zinc sulphate ; 
for steel-plates, solution of copperas or of ammonium chloride; 
for brass, solution of ferric chloride. In place of the baths of 
metallic salts, pure water slightly acidulated with sulphuric, 
hydrochloric, or nitric acid may be used. 

As covering or etching ground, the previously mentioned 
mixture of rosin and wax, or the acid-proof varnish is used. 

Since the current-strength is under perfect control, the etch- 
ing may be carried to any depth desired. Some portions may 
be less etched than others by taking the plate from the bath, 
and, after washing and drying, coating the portions which are 
not to be further etched with lacquer, and returning the plate 
to the bath. 

Printing plates in relief may in this manner be prepared by 
slightly etching the bared design of a copper plate in the gal- 
vanoplastic copper bath, and then bringing the plate as object 
in contact with the negative pole, while a plate of chemically 
pure copper serves as anode. The deposited copper unites 
firmly with the rough copper of the etched plates, and after 
removing the etching ground with benzine or oil of turpentine, 
the design appears in relief. 

Heliography. — The heliographic process, invented by Pretsch, 
and improved by Scamoni, consists in taking by photography 
a good negative of the engraving or other object to be repro- 
duced, developing with green vitriol, reinforcing with pyrogallic 
acid and silver solution, and then fixing with sodium hypo- 
sulphite solution in the same manner as customary for pho- 
tographic negatives. A further reinforcement with chloride of 



GALVANOPLASTY (REPRODUCTION). 631 

mercury solution then takes place until the layer appears light 
gray. Now wash thoroughly and intensely blacken the light 
portions by pouring upon them dilute potassium cyanide solu- 
tion. As in the photographic process, the solution must be 
applied in abundance and without stopping, as otherwise 
streaks and stains are formed. After washing, the plate is 
dried, further reinforced, and finally coated w T ith a colorless 
negative varnish. From this negative a positive collodion 
picture is taken, which is in the same manner developed, re- 
inforced and fixed, the reinforcement with pyrogallic acid 
being continued until the picture is quite perceptibly raised. 
After careful washing, pour upon the plate quite concentrated 
chloride of mercury solution, which has to be frequently re- 
newed, until the picture, at first deep black, acquires a nearly 
white color, and the lines are perceptibly strengthened. Now 
wash with distilled water, next with dilute potassium iodide 
solution, and finally with ammoniacal water, whereby the 
picture acquires first a greenish, then a brown, and finally a 
violet-brown, color. After draining, the plate may be pro- 
gressively treated with solutions of platinum chloride, gold 
chloride, green vitriol and pyrogallic acid, the latter exerting 
a solidifying effect upon the pulverulent metallic deposits. 
The metallic relief is now ready ; the layer is slowly dried 
over alcohol, and the plate, when nearly cold, quickly coated 
with a thin rosin varnish, which, after momentary drying, 
remains sufficiently sticky to retain a thin layer of black lead, 
which is applied with a tuft of cotton. The edge of the plate 
is finally surrounded with wax, and, after being wired, the 
plate is brought into the galvanoplastic copper bath to be 
reproduced. 

Electro-engraving. — Below an outline of Rieder's patented 
process is given, it being supposed that the subject under dis- 
cussion is the production of a die by means of which reliefs 
are to be stamped in metal plates. 

The relief is first produced in a material readily worked, for 
instance, wood, wax, etc., and a copy of it made in plaster of 



632 ELECTRO-DEPOSITION OF METALS. 

Paris. The plaster of Paris plate, which is about £ to f inch 
or more thick, is placed in a metal cylinder in such a manner 
that a plaster of Paris surface of 0.11 to 0.15 inch depth pro- 
jects above the edge of the cylinder. This cylinder contain- 
ing the plaster of Paris model is secured in a vessel containing 
solution of ammonium chloride and a metal spiral connected 
with the negative pole of the source of current. By a suitable 
mechanical contrivance the vessel, together with the cylinder 
containing the model, is pressed against the steel plate con- 
nected with the positive pole. 

The process is now as follows : The porous plaster of Paris 
absorbs to saturation ammonium chloride solution. The steel 
plate first comes in contact with the highest points of relief, 
and the current becoming active, dissolves the steel on the 
point of contact. The ferrous chloride solution which is 
formed penetrates downwards into the capillaries of the plaster 
of Paris, so that fresh quantities of the electrolyte constantly 
act upon the steel plate. Etching thus progresses, and gradu- 
ally every portion of the plaster of Paris model comes in con- 
tact with the steel plate, when etching is finished. 

However, the practical execution of the work is not so 
simple as the theoretical process above described. The carbon 
in the steel and other admixtures, such as silicon, etc., prevent 
uniform etching and must, therefore, from time to time, be 
mechanically removed from the etching surface. For this 
purpose the vessel containing the electrolyte, together with the 
model, has to be lowered, the steel plate taken from the ap- 
paratus and cleansed. It will, therefore, be readily under- 
stood that accurate etching corresponding to the metal can 
only take place when the principal parts, namely, the steel 
plate and model, after cleansing, mathematically occupy ex- 
actly the same place and position as before, so that the model 
presses accurately against the same parts of the steel plate as 
in the beginning of the etching operation. 

Conjointly with Dr. Geo. Langbein & Co., Rieder has con- 
structed an apparatus which works with such precision as to 



GALVANOPLASTY (REPRODUCTION). 633 

fulfill all the above-mentioned conditions, and may be briefly 
described as follows : * The plaster mould is secured by two 
conical wedges to a cast-iron frame upon a vertically moving 
table, the latter being set in motion by an eccentric. Above 
this table is the clamping plate for the steel anode to be etched. 
This clamping plate is also adjustable, and by a suitable con- 
trivance can be set exactly parallel to the model. Cleansing 
of the steel plate is effected by means of a carriage carrying a 
revolving brush and worked by an eccentric ; the brush re- 
ceives water through a perforated pipe, and in addition a 
sponge roller is carried over the model for the purpose of 
acidulating the latter. 

The machine works as follows : By means of the movable 
table the model is without shock and as elastically as possible 
placed against the plate to be etched. After the plate and 
model have been in contact for 15 seconds, the model is lifted 
off and the cleaning process by brushing, etc., is effected. As 
soon as the cleaning carriage is withdrawn, the model is again 
brought against the steel-plate and the operation repeated. 

Each electro-engraving machine is supplied with a model 
casting arrangement, the frames of the machine* being utilized 
for the purpose. 

The dynamo used has an impressed electro-motive force of 
12 to 15 volts, and the current-strength for a plate of 200 x 300 
millimeters is about 50 amperes, when the whole surface of 
the plaster model has been brought in contact with the steel- 
plate. An electro-engraving plant of this kind was exhibited 
at the Paris Exposition in 1900. 

The depth of the etching depends on the time of contact, 
but it may be laid down as a rule that, according to the fine- 
ness of the model 4 or 5 hours are required for a depth of 1 
millimeter. The cleaning process above described may event- 
ually be effected with the assistance of an air compressor. 

* Pfanhauser, Die Herstellung von Metallgegenstiinden auf elektrolytiscken 
Wege und die Elektrograviire, 1903. 



634 ELECTRO-DEPOSITION OF METALS. 

Allowing 12 seconds as the duration of etching, about. 600 to 
800 etching periods must take place in order to etch to the 
depth of 1 millimeter. Experiments made on a large scale 
have proved this method to be very suitable for many pur- 
poses, even if it does not make hand-engravers superfluous. 
For the latter, however, it is an excellent auxiliary for the 
purpose of obtaining engravings absolutely true to nature from 
models in wax, etc., and it allows of the preparation in a very 
short time of engraved dies, plates, etc. The last retouching 
and polishing have to be done by the hand of the engraver, 
because in accordance with the nature of the porous plaster- 
of-Paris model, the etched surface shows but little luster. 
Further details would not come within the compass of this 
work, and interested parties are referred to the firm " Elektro- 
graviire," Leipsic, Saxony, Germany, who has secured the 
patents and constructs the electro-engraving machines. 

B. Galvanoplastic Reproduction of Plastic Objects. 

The reproduction of busts, vases, etc., requires an entirely 
different process of preparing the moulds than that described 
as applied in the graphic arts, the material for moulding de- 
pending on the nature of the original. Besides gutta-percha 
and wax, readily fusible metals, oil gutta-percha, plaster of 
Paris, and glue will have to be considered. If the original 
bears heating to about 230° F., a copy in one of the readily 
fusible alloys given later on may be made. If it will stand 
heat and pressure, it is best to mould in gutta-percha, but if 
no pressure and only slight heat can be used, recourse may be 
had to oil gutta-percha. If neither heat nor pressure can be 
applied, the moulds will have to be executed in plaster of 
Paris or in glue. . The manner of moulding and the material 
to be chosen furthermore depend on whether surfaces in high 
relief or round plastic bodies are to be copied, whether pro- 
jecting portions are undercut, and whether the mould can be 
directly detached, or, if this is not the case, whether the orig- 
inal has to be dissected and moulded in separate parts. 



GALVANOPLASTY (REPRODUCTION). 635 

Regarding the practice of moulding, the reader is referred 
to special works on that subject. Only the main points for 
the most frequently occurring reproductions will here be given. 

Surfaces in relief and not undercut are readily moulded in an 
elastic mass, such as gutta-percha or wax ; however, undercut 
reliefs, and especially round plastic objects, mostly require a 
plaster-of-Paris mould and are generally dissected. The dis- 
section, of course, is not carried further than absolutely neces- 
sary, because the separate parts must be united by a soldering 
seam, which requires careful work, and the seam itself must be 
worked over and made invisible. Hence the section should as 
much as possible be made through smooth surfaces, edges, 
etc., where the subsequent union by a soldering seam will 
prove least troublesome ; cutting through ornaments or 
through portions, the accurate reproduction of which is of the 
utmost importance, should be avoided. Heads and busts are 
always executed in a core mould and in portions, unless the 
entire figure is to be deposited in one piece in a closed mould. 
The section is made either through the center line of the head 
through the nose, which, however, makes the subsequent union 
very troublesome, if the copy is to be an exact reproduction of 
the original, or the mould is divided from ear to ear, which 
has the disadvantage that the deepest part of the mould cor- 
responding to the nose receives the thinnest deposit. It has, 
therefore, been proposed to make two cuts so that three por- 
tions are formed ; one cut from one ear at the commencement 
of the growth of hair to the other ear ; and the second cut from 
one ear in a downward direction below the lower jaw in the 
joint of the head and neck, through this joint below the chin, 
and then upwards to the other ear, and in front of it to where 
the hair begins. In bearded male heads the cut follows the 
contour of the beard and not the joint on the neck behind the 
beard. 

Moulding with oil gutta-percha. — Oil gutta-percha has the 
advantage of allowing moulding without any pressure of the 
largest shield-shaped or semi-circular objects with all the 



636 ELECTRO- DEPOSITION OF METALS. 

imder-cuts, which otherwise can only be accomplished with 
glue. The mould can be readily detached from the original 
as well as from the deposit, which is of great advantage. But 
on the other hand, oil gutta-percha deteriorates by frequent 
use, and sticks to the mould when worked too hot, the result 
being that it is difficult to detach from the original, and, 
besides, air bubbles are formed. However, the heat must 
neither be too slight, otherwise the sharpness of the impres- 
sion would suffer. 

Oil gutta-percha is prepared by heating on the water-bath 
100 parts of gutta-percha, 10 parts of olive oil and 2 parts of 
stearine. 

The original, preferably of copper, should be slightly oiled. 
It is laid upon an iron plate and the latter heated by a flame 
until the original can be just for a moment retained in the 
hand. The oil gutta-percha, previously heated on a sand-bath 
and thoroughly stirred, is then brought in a slow stream upon 
the original. After allowing the oil gutta-percha to congeal 
superficially, the original, together with the heating plate, is 
brought into cold water, where complete congealing soon takes 
place. 

For moulding in the press or by hand with oil gutta- 
percha, the heated mass is poured into cold w ? ater and then 
kneaded to the consistency of stiff dough. 

Moulding with gutta-percha. — To mould round articles in 
gutta-percha, the softened gutta-percha is kneaded with wet 
hands upon the oiled original, or, in order to avoid some por- 
tions receiving a stronger pressure than others, and to insure 
a layer of gutta-perch of uniform thickness upon all parts, 
moulding may also be executed in a ring or frame of iron or 
zinc under a press. For the rest, all that has been previously 
said in regard to moulding in gutta-percha is also applicable. 

Metallic moulds. — The following metallic alloys have been 
proposed for the preparation of moulds : 

I. Lead 2 parts, tin 3, bismuth 5 ; fusible at 212° F. 
II. Lead 5, tin 3, bismuth 8 ; fusible at 183° F. 



GALVANOPLASTY (rP]PRODUCTION). 637 

III. Lead 2, tin 2, bismuth 5, mercury 1 ; fusible at 158° F. 

IV. Lead 5, tin 3, bismuth 5, mercury 2; fusible at 1 27.5° F. 
The advantage of metallic moulds consists in the metal 

being a good conductor of electricity, in consequence of which 
heavy deposits of greater uniformity can be produced than 
with non-metallic moulds which have been made conductive 
by black lead. Nevertheless, they are but seldom employed, 
on account of the crystalline structure of the alloys and the 
difficulty of avoiding the presence of air bubbles. Bottger 
claims that a mixture of lead 8 parts, tin 3, and bismuth 8, 
which is fusible at 227° F., shows a less coarse-grained 
structure. 

Fusible alloys containing mercury should not be. used for 
taking casts of metallic objects — iron excepted — as these will 
amalgamate with the mercury and be injured. Moreover, 
copper deposits produced upon such alloys are very brittle, this 
being due to the combination of the mercury with the de- 
posited copper. 

For moulding with metallic alloys, place the oiled object at 
the bottom of a shallow vessel and pour the liquid metal upon 
it ; or pour the liquid metal into a box, remove the layer of 
oxide with a piece of thick paper, and when the metal is just 
beginning to congeal firmly press the object upon it. 

Plaster- of- Paris moulds are used for making casts of portions 
from originals which are so strongly undercut that a mould 
consisting of one piece could not be well detached from them. 
For taking casts from metallic coins and medals, or from small 
plaster reliefs, it is a very convenient material. The mode of 
procedure is as follows: After the original model, say a 
medal, has been thoroughly soaped or black-leaded, wrap 
round the rim a piece of sufficiently stout paper or thin lead 
foil, and bind it in such a manner by means of sealing-wax 
that the face of the medal is at the bottom of the receptacle 
thus formed. Then place the whole to a certain depth in a 
layer of fine sand, which prevents the escape of the semi-fluid 
plaster of Paris between the rim of the medal and the paper. 



638 ELECTRO-DEPOSITION OF METALS. 

Now mix plaster of Paris with water to a thin paste, take up 
a small quantity of this paste with a pencil or brush and 
spread it in a thin film carefully and smoothly over the face 
of the medal, then pour on the remainder of the paste up to a 
proper height, and allow it to set. After a few minutes the 
plaster heats and solidifies. Then remove the surrounding 
paper, scrape off with a knife what has run between the paper 
and the rim of the medal, and carefully separate the plaster 
cast from the model. If, instead of applying the first layer 
with a brush, the whole of the plaster were run at once into 
the receptacle, there would be great risk of imprisoning air 
bubbles between the model and the mould, which would con- 
sequently be worthless. The mould is finally made impervious 
and conductive according to one of the methods to be de- 
scribed later on. 

The moulding in plaster of Paris in portions, when casts 
from large plastic objects with undercut surfaces and reliefs 
are to be taken, is troublesome work, because each separate 
mould must not only be so that it can be readily separated 
without injury to the original, but must also fit closely to its 
neighbors. Hence thought and judgment are required to see 
of which parts separate moulds are to made, or, in other 
words, in how many parts the mould is to be made. After 
determining on the plan of the work, the mode of procedure 
is as follows : Oil a portion of the object, if it consists of metal, 
or soap it, if of plaster-of-Paris, marble, wood, etc., and appty 
by means of a brush a thinly-fluid paste of plaster-of-Paris, 
taking care that no air bubbles are formed by the strokes of 
the brush. When this thin coat is hard, continue the appli- 
cation of plaster-of-Paris with a horn spatula until the coat 
has acquired a thickness of f to 1 inch, and allow it to harden. 
Then separate the mould, and after cutting or sawing the 
edges square and smooth, replace it upon the portion of the 
original model corresponding to it. Now oil or soap the 
neighboring portions of the model, and at the same time the 
smooth edges of the first mould which come in contact with 



GALVANOPLASTY (REPRODUCTION). 639 

the mould now to be made, and then proceed to make the 
second mould in precisely the same manner as the .first. 
When the second mould is hard, trim the edges and replace 
it upon the model ; the same process being continued until the 
entire original model is reproduced in moulds fitting well to- 
gether. To prevent the finished moulds from falling off, and 
to retain them in a firm position upon the original model, 
they are tied with lead wire or secured with catches of brass 
wire or sheet. When the moulds of the larger portion of the 
model, for instance, one-half of a statue, are finished, the so- 
called case or shell is made, i. e., the backs of all the moulds 
are coated with a layer of plaster-of-Paris which holds them 
together. This case is best made not too thin in order to at- 
tain a better resisting power. 

The entire model having been cast in the manner above 
described, and the moulds provided with the case, the whole 
is completely dried in an oven. 

Rendering plaster-of-Paris moulds impervious. — The next 
operation is to make the plaster-of-Paris impervious to fluids, 
as otherwise by the moulds absorbing the acid copper bath, 
copper would be deposited in the pores of the plaster and the 
moulds be spoiled, while the copy would turn out rough in- 
stead of having the smooth exterior of the model. To render 
plaster-of-Paris and other porous substances impervious, thej 7 
are saturated with wax or stearine, or covered with a coat of 
varnish, the latter process being generally employed for large 
moulds. Apply a coat of thick linseed-oil varnish to the face 
of the mould, and, after drying, repeat the process until the 
mould is considered to be sufficiently impervious. 

Rendering the mould impervious with wax or stearine is a 
better and more complete method. For this purpose place 
the heated mould in a vat filled with melted wax or stearine, 
so that the face does not come in contact with the wax but 
absorbs it by capillarity from the bath. However, as this 
cannot be done in every case, the mould, if necessary, may be 
entirely submerged in the melted wax until no more air- 



640 ELECTRO-DEPOSITION OF METALS. 

bubbles escape. It is then taken from the bath and laid, face 
up, in a drying oven, whereby the wax in melting oozes down 
in consequence of its gravity, the face of the mould being thus 
freed from an excess of wax. 

To prevent the removal of too much wax from the face, the 
mould is cooled off with cold water the moment the excess of 
wax is noticed to have penetrated from the face into the in- 
terior. After drying the mould, the face is coated with gutta- 
percha lacquer, in order to make the high reliefs, which may 
have been too much freed from wax, impervious. Gutta- 
percha lacquer is prepared as follows : 

Bring into a wide-mouthed glass bottle provided with a 
glass-stopper, gutta-percha cut up in small pieces, and fill the 
bottle with a. mixture of equal parts by volume of ether and 
benzol. The bottle is allowed to stand for several weeks in a 
moderately warm room, the contents being frequently shaken. 
In this time as much gutta-percha as the solvent can absorb 
will be dissolved. 

For rendering impervious porous, non-metallic moulds upon 
which copper is later on to be deposited, Greif has patented 
the following process : The impregnating agent consists of 
about 70 parts coal-tar pitch, 20 parts retene (methylpropyl 
phenanthrene), and 10 parts naphthalene. The mixture of 
the ingredients having been melted by steam, the body to be 
impregnated is immersed in the liquid mass, and allowed to 
remain in it a short time to become throughout impregnated. 
An excess of the impregnating agent is readily removed by 
allowing it to drain off. 

Metallizing or rendering the moulds conductive. — Metallization 
by the dry way. The moulds thus varnished or impregnated 
with wax are next rendered conductive with black lead, the 
operation being the same as that for moulds for the graphic arts. 

In some cases metallization by metallic powders is, however, 
to be preferred to black-leading or metallizing by the wet way. 
Metallic or bronze powders are metals in an exceedingly fine 
state of division, of which, for galvanoplastic purposes, pure 



GALVANOPLASTY (REPRODUCTION). 641 

copper and brass powders only are of interest. Since such 
metallic powders adhere badly to waxed surfaces, the mould 
must be provided with a quick-drying coat of lacquer, upon 
which, before it is completely dry, the powder is scattered or 
sifted. When the lacquer is hard a smooth surface is pro- 
duced by going over the mould with a soft brush dipped in 
the metallic powder, an excess being removed by a thin jet of 
water. 

For many undercut or very deep portions which cannot be 
thoroughly manipulated with the brush, metallization with 
black-lead proves insufficient, and recourse will have to be 
had to 

Metallization by the wet way. — This method consists in the 
deposition of certain metallic salts upon the moulds and their 
reduction to metal or conversion to conductive sulphur combi- 
nations. The process in general use is as follows : Apply with 
a brush upon the mould a not too concentrated solution of 
silver nitrate in a mixture of equal parts of distilled water and 
90 per cent, alcohol. When the coat is dry expose it in a 
closed box to an atmosphere of sulphuretted hydrogen. The 
latter converts the silver nitrate into silver sulphide, which is 
a good conductor of the current. For the production of the 
sulphuretted hydrogen, place in the box, which contains the 
mould to be metallized, a porcelain plate or dish filled with 
dilute sulphuric acid (1 acid to 8 water), and add five or six 
pieces of iron pyrites the size of a hazelnut. The development 
of the gas begins immediately, and the box should be closed 
with a well-fitting cover to prevent inhaling the poisonous gas ; 
if possible the work should be done in the open air or under 
a well-drawing chimney. The formation of t'he layer of silver 
sulphide requires but a few minutes, and if not many moulds 
have to be successively treated, the acid is poured off from the 
iron pyrites and clean water poured upon the latter so as not 
to cause useless development of gas. 

It has also been recommended to decompose the silver salt by 
vapors of phosphorus and to convert it into silver phosphide, 
41 



642 ELECTRO-DEPOSITION OF METALS. 

a solution of phosphorus in carhon disulphide being used for 
the purpose. The layer of silver salt is moistened with the 
solution or exposed to its vapors. This method possesses, how- 
ever, no advantage over the preceding one, because, on the one 
hand, the phosphorus solution takes fire spontaneously, and, 
on the other, the odor of the carbon disulphide is still more 
offensive than that of sulphuretted hydrogen. 

A somewhat modified method is given by Parkes as follows : 
Three solutions, A, B, C, are required. Solution A is prepared 
by dissolving 0.5 part of caoutchouc cut up in fine pieces in 10 
parts of carbon disulphide and adding 4 parts of melted wax ; 
stir thoroughly, then add a solution of 5 parts of phosphorus 
in 60 of carbon disulphide, together with 5 of oil of turpentine 
and 4 of pulverized asphalt ; then thoroughly shake this mix- 
ture, A. Solution B consists of 2 parts by weight of silver 
nitrate in 600 of water; and solution C of 10 parts of gold 
chloride in 600 of water. The mould to be metallized is first 
provided with wires and then brushed over with or immersed 
in solution A, and after draining off, dried. The dry mould is 
then poured over with the silver solution (B) and suspended 
free for a few minutes until the surface shows a dark luster. 
It is then rinsed in water and treated in the same manner 
with the chloride of gold solution (C), whereby it acquires a 
yellowish tone, when, after drying, it is sufficiently prepared 
for the reception of the deposit. Care must be taken in pre- 
paring solution A, carbon disulphide which contains phos- 
phorus readily taking fire. 

However, in some cases, either one of the above-mentioned 
methods may leave the operator in the lurch. On the one 
hand, a small accumulation of silver salt solution in the 
deeper places cannot be well prevented, a slightly crystalline 
layer of salt being consequently formed and, on the other, it 
may happen that the layer of silver sulphide becomes without 
discernible reason detached from the mould in the copper 
bath, thus necessitating a repetition of the process. 

In many cases the following method has been successfully 



GALVANOPLASTY (REPRODUCTION). 643 

used : Dilute iodized collodion solution, such as is used for 
photographic purposes, with an equal volume of ether-alcohol, 
and pour this solution quickly and without intermission over 
the mould, the latter being inclined so that all portions of it 
come in contact with the collodion solution, when the mould is 
turned face down to allow an excess to run off. By manipu- 
lating with sufficient rapidity a film of collodion solution re- 
mains upon the mould. This film, at the moment of congeal- 
ing, is exposed for 2 to 3 minutes to the action of a weak 
solution of silver nitrate in water, the operation being best 
effected in a darkened room. The collodion containing potas- 
sium iodide forms with the silver bath, silver iodide, the pre- 
viously clear collodion layer becoming yellowish. In this 
state the mould is taken from the silver bath, washed with a 
weak jet of water to remove an excess of silver solution, and 
then for a few minutes exposed to the sun. By this means a 
reduction of the silver salt takes place, which is rendered still 
more intense by laying the mould in a solution of copperas in 
water, alcohol and glacial acetic acid, in the proportion of 
1.76 ozs. copperas, 1 oz. glacial acetic acid, 0.7 oz. alcohol per 
quart of water. The mould is then rinsed in water and 
immediately brought into the copper bath, the conduction of 
the current to the layer of silver having been first effected by 
means of a few feelers. 

In applying this method it must be borne in mind that the 
collodion layer will not bear rough handling, and injury of it, 
by touching it with the hands or a strong jet of water, or by 
careless application of the conducting wires (feelers), must be 
avoided. When operating with the care required, the results 
are very satisfactory and sure. 

In place of iodized collodion, a mixture of equal parts of 
white of egg and saturated common salt solution may be used, 
the process for the rest being the same as above described. 

Lenoir's process — Galvanoplastic method for originals in high 
relief. — Lenoir's method for reproducing statues in a manner 
approaches in principle to that of the foundry. He begins by 



644 ELECTRO-DEPOSITION OF METALS. 

making with gutta-percha a mould in several pieces, which, 
are united together so as to form a perfect hollow mould of the 
original. This having been done, cover all the parts carefully 
with black-lead. Make a skeleton with platinum wire, follow- 
ing the general outline of the model, but smaller than the 
mould, since it must be suspended in it without any point of 
contact. If the skeleton thus prepared is enclosed in the 
metallized gutta-percha mould, and the whole immersed in the 
galvanoplastic bath, it will be sufficient to connect the inner 
surface of the mould with the negative pole of the battery, and 
the skeleton of platinum wires (which should have no points 
of contact with the metallized surfaces of the mould) with the 
positive pole, in order to decompose the solution of sulphate 
of copper which fills the mould. When the metallic deposit 
has reached the proper thickness the gutta-percha mould is 
removed by any convenient process, and a faithful copy of the 
original will be produced. Lead wires may be substituted for 
the expensive platinum wires. This method requires a knowl- 
edge of the moulder's art, so that good results can only be 
obtained by an experienced hand. 

Gelatine moulds. — Under certain conditions the elasticity of 
gelatine allows of the possibility of its removal from undercut 
or highly-wrought portions of the model, when it reassumes 
the shape and position it had before removal therefrom. But 
gelatine requires that the deposit shall be made rapidly, other- 
wise it will swell and be partially dissolved by too long an 
immersion in the copper bath. 

To make a good gelatine mould, proceed as follows: Allow 
white gelatine (cabinet-maker's glue) to swell for about 24 
hours in cold water, then drain off the water, and heat the 
swollen mass in a water-bath until completely dissolved. 
Compound the glue solution with pure glycerine in the pro- 
portion of 5 to 10 cubic centimeters (0.24 to 0.3 cubic inch) 
of glycerine to 30 grammes (1.05 ozs.) of gelatine, which, 
prevents the gelatine from shrinking in cooling. When some- 
what cooled off", apply the gelatine to the oiled original, which 



GALVANOPLASTY (REPRODUCTION). 645 

must be surrounded with a rim of plaster of Paris or wax, to 
prevent the gelatine from running off; when cold, lift the 
gelatine mould from the model. Before metallizing and sus- 
pending in the copper bath, the mould has to be prepared to 
resist the action of the latter, as otherwise it would at once 
swell and be partially dissolved before being covered with the 
deposit. This is effected by placing the mould in a highly 
concentrated solution of tannin, which possesses the property 
of making gelatine insoluble. 

Brandley gives the following directions for preparing gela- 
tine solution with an addition of tannin, which renders the 
moulds impervious to water : Dissolve 20 parts of the best 
gelatine in 100 of hot water, add ^ part of tannic acid and the 
same quantity of rock candy, then mix the whole thoroughly, 
and pour it upon the model. 

The same object is attained by the use of potassium dichro- 
mate solution in place of tannin solution. In this case, the 
potassium dichromate solution must be allowed to act in a 
dark room, the mould being then for some time exposed to the 
action of the sun. The chrome gelatine layer formed upon the 
surface does not swell up, and is insoluble, at least for the time 
required to cover the mould with copper. Rendering glue 
moulds conductive by means of black-lead is, as a rule, im- 
practicable, and metallization has to be accomplished by the 
wet way in order to effect a rapid formation of the deposit. 
Moulds rendered conductive by black-lead should be rapidly 
covered with copper while the bath is being agitated, because 
a bath in which a considerable quantity of gelatine has been 
dissolved, yields brittle copper, while by a very small quantity 
of it, the density of the deposit is increased. 

Special Applications of Galvanoplasty. 

Nature printing, so named by Mr. v. Auer, Director of the 

Imperial Printing Office at Vienna, has for its object the gal- 

vanoplastic reproduction of leaves and other similar bodies. 

The leaf is placed between two plates, one of polished steel, 



646 ELECTRO-DEPOSITION OP METALS. 

the other of soft lead, and is then passed between rollers, 
which exert a considerable pressure. The leaf thus imparts 
an exact impression of itself and of all its veins and markings 
to the lead, and this impression may be electrotyped, and the 
copper plate produced used for printing in the ordinary way. 
Instead of taking the impression in lead, it is advisable to use 
gutta-percha or wax for delicate objects, which should pre- 
viously be black-leaded or oiled. In the same manner gal- 
vanoplastic copies of laces, etc., may be obtained. 

Elmore produces copper tubes by galvanoplastic deposition 
by allowing the metallic core-bar to revolve slowly between 
the anodes, while a polishing steel is by means of a mechan- 
ical contrivance carried with strong pressure over the deposit, 
whereby the latter is made dense and any roughness removed. 

It would seem that the process for the production of copper 
tubes, profiled hollow copper bodies, etc., patented by Ignaz 
Klein, is better than Elmore's method. The black-leaded or 
metallic core-bars are allowed to roll to and fro upon smooth 
or profiled plates, the so-called milling plates, or the core-bars 
are concentrically arranged around a cylindrical anode and 
allowed with pressure to roll on an exterior round milling sur- 
face. According to this method, the space in the baths can 
be better utilized than in the Elmore process, and the deposit 
shows excellent properties as regards uniform density and 
power of resistance. 

According to Dieffenbach and Limpricht's method (German 
patent 125404) tubes and hollow bodies of copper of great 
toughness and strength are obtained by allowing the metal 
cores, or other cores rendered conductive in a suitable manner, 
to revolve in an acid bath to which fine sand or, better, in- 
fusorial earth has been added. The infusorial earth exerts a 
scouring effect and removes any hydrogen bubbles which may 
have been separated. Experiments made with this process 
yielded copper tubes which on being tested showed excellent 
values as regards strength. 

Corvin's niello. — Corvin has invented a process of producing 



GALVANOPLASTY (REPRODUCTION). 647 

inlaid work by galvanoplasty. The process is as follows : A 
matrice of metal whose surface is finely polished is first made. 
This matrice may be used for the production of numerous 
duplicates of the same kind of object. The incrustations 
(mother-of-pearl, glass, ivory, amber, etc.) are then shaped by 
means of a saw, files and other tools to the form corresponding 
to that which they are to occupy in the design. The side of 
the incrustation which is laid upon the matrice is, as a rule, 
smooth. The shaped incrustations, smooth side down, are 
pasted on to the parts of the model they are to occupy in the 
design. The latter being thus produced, the backs of the 
non-metallic laminae are metallized, and the portions of the 
metallic plate left free are slightly oiled. By now placing the 
matrice thus prepared in the galvanoplastic bath, the copper 
is deposited, not only upon the metallic matrice, but also upon 
the back of the inlaid pieces, the latter being firmly inclosed 
by the deposited metal. When the deposited metal has ac- 
quired the desired thickness, it is detached from the matrice, 
and incrustations with the right side polished are thus ob- 
tained. The laminae are more accurately and evenly laid in 
than would be possible by the most skilled hand-work. 

Plates for the production of imitations of leather. The demand 
for alligator and similar leathers is at the present time greater 
than the supply, and, therefore, imitations are made by press- 
ing ox-leather, the plate being prepared by galvanoplasty, as 
follows : A large piece of the natural skin or leather is made 
impervious to the bath by repeated coatings with lacquer, and, 
when completely dry, secured with asphalt lacquer to a cop- 
per or brass plate. The leather is then black-leaded, and, after 
being made conductive by copper wire or small lead plates, 
brought into the copper bath. When the copper deposit has 
acquired the desired thickness, the plate is further strength- 
ened by backing with stereotype metal. 

Incrusting galvanoplasty. — This term may be applied to the 
process by which a thick coat of copper, or of another metal, 
is deposited upon an article. This deposit, however, is not 



648 ELECTRO-DEPOSITION OF METALS. 

detached from the original, as in reproduction-galvanoplasty, 
but remains upon it, the object being, as a rule, to embellish 
the article or to give non-metallic articles the appearance of 
metallic ones. 

Non-metallic objects to be coated have also to be rendered 
impervious to the electrolyte, great care being required in this 
respect, since in case the acid copper bath penetrates into the 
article to be coated, the deposit would later on effloresce and 
peel off. 

The objects may be rendered impervious by one of the 
methods mentioned above, it being best, however, first to heat 
them, as for instance, terra-cotta busts, and then place them in 
melted wax, or mixtures of wax and paraffine. By heating 
the greater portion of the air is expelled from the pores, the 
wax thus penetrating better and closing the pores. An excess 
of wax is removed by draining off in a warm room (air-bath), 
and when cold the objects are coated with gutta-percha lacquer 
and metallized with black-lead. 

However, it will frequently be impracticable to reach every 
portion with the black-lead brush, and in this case it is recom- 
mended to effect metallization by the wet way, as follows : 

Coat the articles, previously rendered impervious, with a 
thickly-fluid solution of shellac in alcohol, and allow them to 
become thoroughly dry. Then immerse them for one minute 
in saturated silver-nitrate solution in 4 parts of water and 6 
parts of alcohol, and allow them to drain off. Bring the arti- 
cles, while still moist, into a vessel which can be closed air- 
tight, and introduce sulphuretted hydrogen. A thin layer of 
silver sulphide will in a few minutes be formed, when the arti- 
cles are taken from the vessel and allowed to dry, the same 
manipulation being once or twice repeated. By operating in 
this manner, non-success is next to impossible, because when 
the object is immersed in the alcoholic silver-nitrate solution, 
the coat of lacquer is superficially softened and absorbs silver 
nitrate, which after its conversion into silver sulphide adheres 
very firmly after drying, so that the layer of it becomes very 



GALVANOPLASTY (REPRODUCTION). 649 

seldom detached in the bath. Should this nevertheless hap- 
pen, it is generally caused by the objects not having been 
thoroughly dried between the separate operations. 

Large objects which cannot be immersed will have to be 
carefully brushed over with the solutions, or the latter be 
poured over them. According to the nature of the objects to 
be coated, the process may have to be somewhat modified, or 
one of the methods already described will have to be employed. 
This will soon be learned by experience. 

Copper bath and current conditions. — Deposits for incrusting 
galvanoplasty should be effected with very slight current- 
densities in order to avoid roughness and a coarsely crystal- 
line structure of the deposft. For many delicate objects to be 
coated with copper, the use of the cell-apparatus is therefore 
advisable. 

Neubeck has investigated the work. in the cell-apparatus 
and its application to encrusting galvanoplasty, and has found 
a copper bath which contains in 100 quarts, 44 lbs. of crys- 
tallized blue vitriol and 13.2 lbs. of sulphuric acid of 66° Be., 
to be especially valuable for the purpose. 

In place of zinc, he used iron plates or iron tubes, and as 
solution, one of sodium sulphate with the addition of a few 
drops of sulphuric acid. The current generated by this ar- 
rangement produces a very finely crystalline deposit free from 
roughness and efflorescences. 

Additional manipulation of the deposits. — The deposits of 
copper produced by one or the other method require, as a 
rule, additional mechanical manipulation to give the outlines 
greater sharpness, and to the whole a more pleasing appear- 
ance. This is done by chiseling to make, for instance, with 
busts, the eyes, nose, ears, etc., more prominent. Scratch- 
brushing, brushing, and polishing are applied if luster is to be 
imparted to the deposits as is required for sufficiently effective 
nickeling, gilding, etc. 

Laces and tissues are, according to Philip, impregnated with 
melted wax, and after removing an excess with blotting-paper, 



650 ELECTRO-DEPOSITION OF METALS. 

they are made conductive by black-leading with a brush. Tt 
is, however, preferable to metallize such delicate objects by 
the wet way, employing one of the methods previously de- 
scribed. 

Grasses, leaves, flowers, etc., are first dried and their former 
shape and elasticity restored by placing them for a consider- 
able time in glycerine. They are then several times immersed 
in gutta-percha lacquer, and metallized with silver nitrate 
solution and sulphuretted hydrogen, or according to one of the 
other processes described. 

Wooden handles of surgical instruments are provided with a 
galvanoplastic deposit of copper to adapt them to antiseptic 
rules. The wood has to be protected from the bath-fluid pen- 
etrating into it, by remaining for a considerable time in 
melted wax or in a solution of wax or paraffine in ether, as 
otherwise the copper-deposit formed will be broken by the 
wood swelling. Metallization is effected by dusting the wood 
thus prepared with black lead or bronze powder, or by the 
wet way. The deposit .is, as a rule, ground, polished, and 
then nickeled. 

Busts and other objects of terra-cotta, stoneware, clay, etc., are 
immersed in melted wax and,. after removing an excess of 
wax, coated with gutta-percha lacquer. If there is no obstacle 
to black-leading, this method may be used for metallization, 
otherwise recourse will have to be had to one of the processes 
previously described. 

When the copper deposit is finished the objects should be 
thoroughly soaked in water, and then for a few hours placed 
in a 5 per cent, yellow prussiate of potash solution for the 
neutralization of any bath-residue which may still remain in 
some of the pores. 

To bring out sharp outlines, especially when the deposit is 
quite thick, the coppered busts and other objects are chiseled, 
scratch-brushed, and polished. They receive, as a rule, a 
patina, according to one of the methods given in Chapter 
XIV, or are brassed, silvered, or gilded. 



GALVANOPLASTY (REPRODUCTION). 651 

The mercury vessels of thermometers for vacuum and distilling 
apparatus are as a protection given a galvanoplastic deposit of 
copper. This is effected in the most simple manner by coat- 
ing the glass with copal lacquer and black-leading the layer 
of lacquer, or applying bronze powder. The glass may also 
be matted by the sand blast, or with fluoric acid, and directly 
black-leaded, the black-lead adhering well to the matted glass 
surface. 

Mirrors are coppered to protect the thin layer of silver from 
injury. For the success of coppering in the acid copper bath 
without danger of the film of silver becoming detached, it is 
necessary to use a weaker bath of at the utmost 8° to 10° Be. 
with 1 per cent, of free sulphuric acid, and to deposit with a 
very slight current-density. 

Glass and porcelain ware, for instance, tumblers, bowls, coffee 
and tea sets, when furnished with galvanoplastic decorations in 
copper or silver, produce beautiful effects. However, metalli- 
zation by one of the processes thus far described is not practi- 
cable, the high reliefs having to adhere firmly to the base, so 
as not to become detached by cleansing or wear. 

Metallization of the portions to be coated is effected by 
painting the arabesques, flowers, monograms, etc., with solu- 
tion of Dutch gold, factitious silver, or platinum, and after dry- 
ing, burning-in in a muffle at a dark red heat. A lustrous 
layer of metal firmly fused together with the glaze is thus 
obtained and is without further preparation fit for coppering 
or silvering. Still greater solidity is attained by triturating 
conducting silver enamel with lavender oil upon a palette to 
a mass of the consistency of paint, applying the latter with a 
brush and burning-in in the muffle. In addition to pure 
silver, the enamel contains fluxing agents which effect a firm 
union of the silver with the porcelain or glass. After burn- 
ing-in, the decorations are gone over with a fine copper brush 
and, the conduction of the current to the metallized portions 
having been effected by means of fine copper wires, the objects 
are brought into the galvanoplastic bath. 



652 ELECTRO-DEPOSITION OF METALS. 

Mr. A. A. Le Fort* gives the following process for "silver 
deposit" on glass and china, which, if followed according to 
directions, will be found satisfactory in every way. The color 
will be found a clear white which is necessary on glass objects, 
when the work is fixed properly and being fused into the 
glass or china, will make a firm body that will hold the de- 
posited silver, so that there will be but a very small loss in 
the plating and finishing operations due to the silver (failing) 
or peeling off, while the loss is very large when the proper 
metallic paint or painting solutions are not employed. The 
formula for the metallic paint, which must be weighed ac- 
curately, is as follows : 

"Metallized silver" 4 ozs., boracic acid 4 dwt., potassium 
nitrate 4 dwt., powdered flint 4 dwt., powdered glass 4 dwt., 
soda ash 4 dwt., red lead 4 dwt., calcined borax 8 dwt. 

While the named ingredients are used in all paints, the 
weight of each may vary in different formulas, but the above 
will be found to be one of the best in use. In order to get the 
silver ready for use in the paint, it must be treated as follows, 
which is called metallizing : Either take fine silver chloride, 
or else cut down your own silver in the usual way, namely, 
one part water and one part nitric acid, in a hot water bath, 
precipitate in the usual way with common salt, wash the 
chloride four or five times, then put the chloride in a glass or 
porcelain bowl, and cover with a solution of two parts sulphuric 
acid to seven parts of water. Then cut common sheet zinc 
into sirips of about one-half inch in width and four or five 
inches in length, and put them in the silver chloride and the 
diluted sulphuric acid, stir occasionally and keep on adding 
zinc until a gray or brownish-colored precipitate of metallic 
silver is formed. Wash thoroughly until free from acid, test- 
ing with blue litmus paper to make sure. After the silver is 
washed, it is necessary to dry it perfectly, by drying it in a 
porcelain or other suitable vessel over a sand-bath. Make 

* Metal Industry, February, 1913. 



GALVANOPLASTY (REPRODUCTION). 653 

sure that it is perfectly dry, so that there will be no error in 
weighing when making up the paint. If the silver is damp 
the weight will not be correct to conform with the other in- 
gredients in the formula. 

After weighing all the ingredients named in the formula, 
mix together, then thin down with oil of turpentine, grind in 
a paint mill, which is made for that purpose, or grind by 
hand, with a glass " muiler " on a heavy glass or stone, which 
can be procured from most art or paint dealers. The grind- 
ing by hand is a long and tedious operation, as it takes a long 
time to do the work properly, for the paint has to be ground 
very fine — the finer, the better the finish will be and the easier 
to handle, when putting on the designs. At any rate, the in- 
gredients must be fine enough to be mixed thoroughly, as if 
too coarse the ingredients in the paint would divide; that is, 
the silver, glass and flint being very coarse would not combine 
correctly with the other powdered ingredients. A good way 
to grind the paint, which saves the cost of a paint mill and 
is just as satisfactory, is to make a small barrel with wooden 
strips, that will hold a common quart fruit jar, and is made 
in the form of a tumbling barrel. This is run by simply 
placing a belt over the shafting and around the barrel. Place 
the paint in the jar with about fifteen or sixteen glass marbles 
of different sizes, from one-half to one inch in diameter. Do 
not make the paint too thin ; cover the jar tightly, place it 
inside of the barrel and pack around with old cloth or rags, to 
stop the jarring or breaking of the jar. Let the barrel run for 
a day or two. The marbles will grind the paint to a fineness, 
without any cost for labor, that could not be obtained by hand 
in several hours. After the paint is ground fine enough, let 
it settle to bottom of jar, and pour off the surplus turpentine. 
This paint (take only what is required for four or five hours' 
work, so that there will be no waste) is then mixed with "fat 
oil of turpentine " (about one part of oil to five or six parts of 
paint) on a glass surface or artist's palette with a palette knife ; 
then thin to proper consistency with oil of turpentine by dip- 



654 ELECTRO-DEPOSITION OF METALS. 

ping the decorating brush in same and working it out on the 
palette. The paint should be mixed or stirred up regularly 
while in the act of decorating, to keep it uniform ; as the oil 
comes to the top, and as the color of the paint is brownish, it 
would be hard to tell whether the lines were painted with 
simply the oil or the paint body. 

Firing. — The second operation is the firing, which proceeds 
as follows : After the work is decorated let it stand five or six 
hours before firing, so that it is partly dry ; then place in the 
oven, light one burner of the gas oven (which is generally used 
for this class of work) ; light a second burner in about five 
minutes, and the rest of the burners at about the same inter- 
vals, so that the heat will start gradually, and not make the 
paint blister or crack, which would be the case if a strong heat 
was applied too quickly. After all the burners are started, it 
will take from one to one and one-half hours to fire work, 
according to size of oven used, but the operator will have to 
try a few pieces, then use his own judgment as to when work 
is properly fired. After foiir or five trials he should be able 
to get correct results. The oven should be in a dark place, or 
in a room that can be darkened when the oven is in use, so 
that the operator can get the right light (when looking at the 
work being fired) through the openings in door of oven to see 
if proper heat is at hand. Heat the oven until the bottom, 
top and sides are at a cherry-red heat, when the paint is then 
properly fused into the glass. Turn off the gas quickly by 
shutting off the cock in the feed-pipe, then let the work cool 
off gradually. Do not open the door of the oven for some 
time — two or three hours — as the cold current of air would 
crack the hot glass. When cool enough to handle, take out 
carefully ; keep the fingers or hands off the painted parts, as 
they would leave marks on the paint, which would be liable 
to blister when plating. 

Now wire the work by making connections, directly on the 
painted parts. Some designs which are not connected will, 
of course, have to have a separate wire on each part, but most 



GALVANOPLASTY (REPRODUCTION). 655 

designs are made so that one connection is all that is re- 
quired. After the work is wired, it is then ready for the plat- 
ing bath without any other process of cleaning, brushing or 
striking up. As the silver must be deposited very slowly, it 
takes between twelve to twenty-four hours for a proper deposit, 
according to the grade of work, the articles which have to be 
engraved to bring out the designs taking the longer time, as 
all that is required for plain or scroll designs is just enough 
silver to stand the finishing operations. The plating solution 
should be composed of not less than 6 ounces silver, and not 
more than 1 or 1J ounces of free cyanide to the gallon. If 
the solution is too light in metal or too strong in cyanide, the 
work will be very hard to finish, and the silver being too 
brittle would raise up from the edges of the painted surface in 
the solution or in the finishing. As it requires such a long 
time for plating, it is really necessary to run plating baths 
with storage batteries during the night to make any headway, 
that is, run the dynamo while the power is going, then switch 
on to the batteries until the work is fully plated. Thus the 
work does not have to be removed from the plating tank at 
night and returned to solution the next day, as that would 
require the cleaning, rewiring and striking up of the work in 
order not to have any failed or peeled pieces. Every particle 
of space in the plating tank should be utilized in order to get 
in as- many pieces of work as possible in every batch, and 
twenty-five to thirty amperes are all that are required for a 
batch of seventy-five or eighty pieces of mixed work; as the 
plating surface is very small even with a full batch of work. 
After the work is plated it is then sand-buffed, cut down with 
tripoli or other cutting-down rouge, washed in benzine, en- 
graved, then colored in the usual way ; that is. finished, the 
same as sterling or silver-plated hollow ware. The quality of 
glass used must also be considered, for some glass will turn 
yellow before the proper heat is reached to fuse the paint, or 
else will get out of shape during the firing. Imported glass 
always gives best results, while thin articles of American glass 



656 ELECTRO-DEPOSITION OE METALS. 

are fairly satisfactory. The heavy, thick glass gives very poor 
results. China will stand and requires more heat in firing 
than glass, so it is advisable to fire china and glass separately 
to obtain the best results. 

Umbrella and cane handles of celluloid are decorated with a 
metallic deposit by means of galvanoplasty. The simplest 
mode of metallizing them is to paint the decorations with a 
mixture of bronze powder and acetone. On the point of con- 
tact, the acetone dissolves a small quantity of celluloid, the 
latter thus becoming quite firmly united with the bronze pow- 
der. After drying, an excess of non-adhering powder is re- 
moved with a brush, and the objects are then brought into the 
copper bath. 

Baby-shoes for a keep-sake, are coppered by galvanoplasty, 
and the deposit is patinized or silvered. Metallization is best 
effected by applying several coats of copal lacquer, and black- 
leading the layer of lacquer on the outside, while the inside, 
which is more difficult of access, is made conductive by means 
of bronze powder or by the wet way. 

Carbon pins and carbon blocks for electro-technical purposes 
are frequently coated with copper in order to effect a more 
sure metallic contact in their mountings. The carbons are 
impregnated with wax so as to prevent the blue vitriol solu- 
tion from penetrating. The} r are then brushed with quick- 
lime and without further preparation brought into the bath. 

Rolls of steel and cast-iron, pump-pistons, etc., are first pro- 
vided with as thick a deposit as possible in the cyanide cop- 
per bath and then brought into the galvanoplastic acid copper 
bath. With a bath at rest the current-density should not ex- 
ceed 30 amperes per square meter, but with an agitated bath 
up to 120 amperes may be used. 

Steel gun barrels for marine purposes are treated in the same 
manner, after all the portions which are not to receive a de- 
posit of copper, have been thoroughly covered with a mixture 
of wax, mastic and red lead. 

Candelabra, stairs and structural parts of buildings of rough 



GALVANOPLASTY (REPRODUCTION). 657 

castings require a somewhat modified treatment. While the 
rolls and steel gun-barrels previously referred to are always 
turned smooth, rough iron castings are used for the above- 
mentioned purposes, and the production in the potassium 
cyanide bath of a copper deposit of such thickness as not to 
corrode the basis-metal in the acid copper bath is frequently 
connected with difficulties. In a plant recently furnished by 
Dr. Geo. Langbein & Co. for coppering rust-proof, and then 
brassing structural parts of a postoffice building in Mexico, 
the following plan was adopted : The rough castings were first 
carefully cleaned by means of a sand blast and then heavily 
nickeled ; upon this nickel coating the 1 millimeter thick cop- 
per deposit could without risk be produced in the acid copper 
bath. The parts were then thoroughly rinsed, dried, bright- 
ened with a brush and emery and, after carefully freeing from 
grease, electrolytically provided with a heavy deposit of 
bronze, and patinized. 

It is believed sufficient examples of the uses of galvanoplasty 
have here been given. It allows of the most varied applica- 
tions, and by studying the special processes described above, 
the reader will be in a position to find out the most suitable 
method for every other contingency. 

II. Galvanoplasty in Iron (Steel). 

Under " Deposition of Iron," the galvanoplastic produc- 
tion of heavy detachable deposits of iron has already been 
referred to. 

Serviceable iron electrotypes w r ere first produced about 1870, 
by Klein of St. Petersburg, and used for printing Russian bank 
notes. Their preparation was, and is still, very troublesome, 
success depending on the fulfillment of many conditions, so 
that, notwithstanding continued experiments and the expense 
of much labor, the former expectation of entirely supplanting 
electrotypes in copper by cliches in steel has thus far not been 
realized. 

The bath used by Klein, and still employed for this purpose, 
42 



658 ELECTRO-DEPOSITION OF METALS. 

consists of a 10 per cent, solution of a mixture of equal parts 
of ferrous sulphate (green vitriol) and magnesium sulphate 
(Epsom salt). The solution has a specific gravity of 1.05. To 
obtain successfully a serviceable electrotype from an original, 
for instance, from a copper plate, which should previously be 
silvered and coated with" a thin layer of silver sulphide bj' 
means of sulphuretted hydrogen, the following conditions have 
to be fulfilled, according to Klein's statement: The bath must 
be kept absolutely neutral, which is effected by suspending in 
it linen bags filled with magnesium carbonate, and the cur- 
rent-strength must be so regulated that absolutely no evolution 
of hydrogen is perceptible on the anodes. Further, the plates 
are every half hour to be taken from the bath and rinsed with 
a powerful jet of water to remove any adhering gas-bubbles. 
Care must be taken during this process that the plates do not 
become dry, since fresh layers do not adhere well upon plates 
which have become dry. 

For the removal of adhering gas-bubbles, it has also been 
proposed frequently to pass a feather over the plates. 

It may here be mentioned that Lenz found a not incon- 
siderable content of hydrogen in iron deposits, and also car- 
bonic acid, carbonic oxide and nitrogen in varying quantities. 
However, examinations made by Dr. Geo. Langbein estab- 
lished positively only a content of hydrogen, and it would 
seem that this hydrogen, which is absorbed and tenaciously 
retained by the deposit, is the cause of all the difficulties 
encountered in the production of heavy iron deposits. 

If, however, the occlusion of hydrogen is regarded as the 
cause of the mischief, ways and means to counteract it as much 
as possible may be found in the fact that iron deposited with 
greater current-density is more brittle, shows a greater ten- 
dency to peel off in the bath, and contains a larger quantity 
of hydrogen than a deposit produced with slighter current- 
density. 

In this respect experience gained in the electrolytic refining 
of copper shows us the May in so far that for the production 



GALVANOPLASTY (REPRODUCTION). 659 

of heavy deposits of iron, the bath must be kept in constant, 
vigorous agitation, to remove, on the one hand, layers of fluid 
poorer in metal from the cathode, and, on the other, to force, 
by the agitation, the gas-bubbles adhering to the cathode to 
escape. Further, deposition must be effected with so slight a 
current-density that no evolution of hydrogen is perceptible 
on the cathode, and a current-density of 0.25 ampere may be 
designated as the maximum per 15J square inches, with which 
heavy deposits of iron can be produced. 

To counteract the spoiling of the deposits, further precau- 
tionary measures are, however, necessary, especially heating 
the electrolyte, and from time to time interrupting the current. 
In heated baths the escape of the gas is facilitated, especially 
when the electrolyte is agitated, and hence adhering gas- 
bubbles cannot remain long in one place. A constantly-re- 
peated interruption of the current is of advantage and effective, 
because metallic parts covered with a minimum quantity of 
hydrogen cannot be coated with a fresh deposit until the hy- 
drogen is removed by the agitation of the heated electrolyte. 
Hence the interruption of the process of deposition would give 
opportunity and time for the removal of the gas molecules 
before further deposition takes place, and without a knowledge 
of the more intimate processes, Klein succeeded in affecting 
the interruption of the deposit, by taking the plates at short 
intervals from the bath and removing the adhering gas by a 
powerful jet of water. 

With the present state of galvanoplasty it is not necessary 
to follow Klein's primitive method, and it would be more prac- 
tical to provide the positive conducting rod of the bath with a 
contrivance which mechanically effects the interruption of the 
current. Suppose upon such a metallic conducting rod is 
mounted a copper or brass wheel, which is secured to a pulley 
and revolves around the conducting rod, and half of the 
periphery of which is insulated, and that upon the rod drags 
a metallic brush which effects the transmission of the positive 
current. Now, it will be seen that while the contact-wheel is 



660 ELECTRO-DEPOSITION OF METALS. 

revolving, current is introduced only one-half the time and 
not during the other half, and that by the rapidity of revolu- 
tion of the contact-wheel, the number of interruptions of the 
current can be varied at will. 

Since Neubeck has in a relatively very short time produced 
in hot baths, deposits 1 to 2 millimeters thick, of coherent 
form and good quality, the possibility is presented of making 
steel electrotypes in an indirect way by obtaining first from 
the impression a copper electrotype, from this a negative in 
copper, and after silvering the latter, producing a heavy 
deposit of steel upon it. 

It may also be expected that by complying with the above- 
mentioned conditions and the discovery of new methods, it 
will be possible directly to produce steel electrotypes upon 
moulds of gutta-percha or wax as is now successfully done 
with nickel. 

It is well known that electrolytically deposited iron pos- 
sesses great hardness, and that such deposits well deserve the 
name of steel deposits, their hardness being greater than that 
of iron, and approaching that of steel. This feature cannot 
be explained otherwise than by the hydrogen absorbed by the 
deposit. Hence it will be seen that, on the one hand, this 
absorption of hydrogen has an injurious effect upon the sep- 
aration of iron, while, on the other, it imparts to the deposits 
the most valuable property of great hardness. It would seem 
that the quantities of iron first deposited upon the mould are, 
and can be, richer in hydrogen in order to impart to the 
printing surface the utmost possible hardness. However, in 
further strengthening and augmenting the deposit, our efforts 
must be directed, by the reduction of the current, to deposit 
strengthening layers as free from hydrogen as possible. 

The question now arises, whether it is of greater advantage 
to steel a copper electrotype in order to increase its power of 
resistance, or whether it is better to produce an iron electrotype 
and to strengthen its back in the acid copper bath. If the 
above expressed view that the layers of iron first deposited are 



GALVANOPLASTY (REPRODUCTION). 661 

richer in hydrogen, and therefore harder, is correct, the prefer- 
ence must be given to iron electrotypes, because with steeled 
copper electrotypes the softer layers are exposed to wear, while 
the harder layers lie upon the copper plate. The reverse 
is the case with an iron electrotype, the first deposit, rich in 
hydrogen, forming the printing face. 

However, on the other hand, steeled copper electrotypes 
have the advantage that, when worn, the old deposit of iron 
can be readily removed by dilute sulphuric acid, and the elec- 
trotypes resteeled, while worn iron electrotypes have to be 
renewed. 

III. GALVANOPLASTY IN NlCKEL. 

Although by the electro-deposition of nickel, electrotypes are 
rendered fit for printing with metallic colors, which attack cop- 
per, and their power of resisting wear is increased, the latter 
advantage can to the fullest extent be obtained only by a thick 
deposit. However, this always alters the design somewhat, 
especially the fine hatchings, this being the reason why in 
nickel-plating electrotypes a deposit of medium thickness is as 
a rule not exceeded. If a hard nickel surface is desired, with- 
out injury to the fine lines of the design, the layer of nickel 
has to be produced by galvanoplasty, and the deposit of nickel 
strengthened in the copper bath. 

But upon black-leaded gutta-percha or wax moulds a nickel 
deposit can only be obtained in fresh baths. The deposit, 
however, is faultless only in rare cases, it generally showing 
holes in the depressions. Hence the object has to be attained 
in a round about way, the mode of procedure being as follows : 
An impression of the original is taken in gutta-percha or wax, 
and from this impression a positive cliche in copper is made. 
The latter is then silvered, the silvering iodized as previously 
described, and a negative in copper is then prepared from this 
positive. The negative is again silvered, iodized, and then 
brought into a nickel bath, where it receives a deposit of the 
thickness of stout writing paper. It is then rinsed in water, 



662 ELECTRO-DEPOSITION OF METALS. 

and the deposit immediately strengthened in the acid copper 
bath. For the rest, it is treated like ordinary copper deposits. 

If for the production of the nickel electrotype, a nickel bath 
of the composition given on p. 266 and heated to between 
185° and 194° F. is used, deposition may be made with high 
current-densities — 5 amperes and eventually more — so that a 
thickness of 0.2 millimeter is in about 1\ hours attained. 
This deposit is slightly coppered in the acid copper bath and 
backed. 

In this manner nickel electrotypes of 15.74 X 11.81 inches 
have been produced, but as will be seen for the purposes of 
printing houses, the process is too troublesome and time-con- 
suming, by reason of the necessary production of the copper 
matrices. Hence the direct method of deposition upon black- 
leaded gutta-percha or wax moulds is decidedly to be preferred. 

This direct method requires a cold nickel bath, which yields 
heavy deposits without the nickel rolling off, and for deposits 
of a thickness suitable for printing, a few contrivances to pre- 
vent spontaneous detachment of the nickel from the matrix. 
The electrolyte, according to patent No. 134736 given on page 
267 is applicable to this purpose. With this electrolyte, de- 
posits of 6 millimeters' thickness were without trouble pro- 
duced at the ordinary temperature upon gutta-percha. In 
testing other nickel baths described or patented, not a single 
one was found which allowed of obtaining useful nickel de- 
posits directly upon the matrices, the nickel always rolling 
off, and when the latter drawback was prevented by suitable 
means, it was impossible to obtain a deposit of more than 0.05 
millimeter thickness, cracks being formed in the center. 

In working with this direct process of deposition, it is abso- 
lutely necessary always to keep the nickel bath slightly acidu- 
lated, because in a neutral or alkaline electrolyte the deposit 
becomes readily rough and forms with a dark color, which is 
an indication of the formation of sponge. It is also of advan- 
tage to keep the electrolyte constantly agitated. By reason of 
the oxidation of the ethyl-sulpho combinations which takes 



GALVANOPLASTY (REPRODUCTION). 



663 



place, agitation, however, must not be effected by blowing in 
air, but by mechanical means, or eventually by blowing in 
carbonic acid. 

An electro-motive force of 2.2 volts and a current-density of 
0.2 to 0.3 ampere proved most suitable for the production of 
the above-mentioned nickel electrotypes of 6 millimeters in 
thickness. The current output — about 70 per cent. — was not 
particularly favorable, this being, however, of little importance 
as compared with the advantages offered by the use of this 
electrolyte. 

It has previously been mentioned that in order to obtain 



Fig. 152. 



Fig. 154. 



Fig. 155. 




' ''js /,,/,/',// ', /// /■ 



:%%%''%'/>■ 
'&&{*/.&&. 



v '"''////"/ '4'w:'/, 

W///7////'' ""'/,?. 



','/'/<■''"',/ ///"/y'i 

', ', '//"/' C'. > vs/, 4 S 
'//, '',///,■>///,//,/ ''A 

"v', i'//''/' '"'//■ 

V'/p/'//'//'/"/', 

"''/'/'/if**. 



Fig. 153. 



deposits of greater thickness upon gutta-percha or wax, a few 
contrivances are required to prevent the deposit from rolling 
off. With the use of gutta-percha matrices there is less danger 
of rolling off than with that of wax moulds, the tendency to 
rolling off being much earlier shown by the latter. However, 
in order to prevent failures, it is advisable not to omit these 
devices even when working with gutta-percha matrices. 

According to the patent specification, a groove undercut 
towards the design and at a distance of about 3 millimeters 
from it, is made all round, and another such groove at a further 
distance of about 3 millimeters, as shown in Fig. 152 in front 
view, and in Fig. 153 in section. 



664 ELECTRO-DEPOSITION OF METALS. 

The object of this contrivance is that upon the careful ty 
black-leaded grooves, nickel continuous with the nickel upon 
the design is also deposited, and by reason of the undercutting 
towards the design the nickel is thus prevented from rolling 
off or becoming detached if, in consequence of the occlusion ot 
hydrogen, the deposit shows a tendency to bend up. 

According to the above-mentioned patent, the same effect 
may also be attained by firmly securing a metallic edge all 
round the design. While the nickel deposit cannot become inti- 
mately attached to the black-leaded, but otherwise non-metallic 
surfaces of the gutta-percha or wax matrices, it adheres very 
firmly to the metallic edge, rolling off being thus prevented. 
Dr. Langbein used thin brass strips, 0.1 millimeter thick and 
5 millimeters wide which, as shown in Figs. 154 and 155, were 
secured by small pins either to the impressed surface or to the 
sides. Wires wound round the four sides of the matrix and 
lying everywhere closely upon its black-leaded surface, may be 
used in place of metal strips. It is advisable to place the 
metal strips in a heated state upon the matrix and press them 
gently into the matrix-material so that their surfaces lie per- 
fectly level with the surface of the impression. The matrix 
and the metal edge having been carefully black-leaded, the 
outside of the latter is brushed over with a rag moistened with 
potassium cyanide solution, care being taken not to damage 
the black-leading of the metal towards the design. Then rinse 
the matrix with alcohol and suspend it at once in tie nickel 
bath, the latter being kept at rest until the matrix is^covered, 
and then agitated. 

Nickel matrices. — In casting type from copper matrices, the 
latter oxidize quite rapidty, in consequence of which the edges 
and lines especially lose sharpness, while the surfaces become 
scarred. As early as 1883, Weston mentions in his English 
patent 4784, the possibility of obtaining heavy deposits of solid 
nickel, and that this invention is valuable for the production 
of electrotypes, which without doubt includes electrolyticalty 
prepared matrices for casting type, the influence of the tern- 



GALVANOPLASTY (REPRODUCTION). G65 

perature of the liquid metal upon such nickel matrices being 
so slight that they do not warp, etc. 

Notwithstanding the fact that thus the employment of an 
electrolytically-produced casting matrix of nickel was known, 
the " Aktien-Gesellschaft fiir Schriftgiesserei " obtained a pat- 
ent, the characteristic feature of which is that zinc can be 
directly cast around the face " without further galvanoplastic 
reinforcement." 

Hence the above-mentioned patent cannot include such 
nickel matrices in which by the deposition of nickel the face 
is produced of a thickness which by itself is insufficient to 
allow of the deposit being detached from the original without 
fear of bending or breaking, the deposit requiring absolutely 
to be reinforced to the customary thickness by a galvano- 
plastic deposit of copper. It is obvious that a thickness of 
0.1 to 0.25 millimeter of nickel suffices to withstand the 
effect of temperature and, when reinforced by copper, also the 
pressure in casting in the machine. Reinforcement of the 
casting of the back with copper has, however, the further 
advantage that in casting zinc around the face, the zinc alloys 
to a certain degree with the copper casting, thus uniting 
firmly with it, which is not the case when zinc is cast around 
the pure nickel face not enveloped by copper, nickel not 
entering into a solid combination with zinc. 

Matrices electrolytically produced from cobalt also cannot 
be claimed under the above-mentioned patent. In hardness, 
cobalt is equal to nickel and resists the hot type-metal as well, 
possessing therefore all the properties required for casting 
matrices. 

The most suitable material for such matrices would be an 
alloy of nickel and cobalt such as has been described on p. 
312 as hard nickel alloy. 

In order to effect an intimate union of the copper casing 
with the nickel, the nickel deposit when taken from the nickel 
bath has to be brushed over with nitric acid, rinsed, and 
without delay brought into the copper bath. 



666 ELECTRO-DEPOSITION OF METALS. 

The omission of these manipulations, which require dex- 
terity, may have been the cause why no more favorable results 
were obtained by former experiments to leinforce thinner 
nickel deposits by copper to a thickness of 2 millimeters, the 
nickel deposits becoming detached from the copper when the 
matrix was in use. If, however, in accordance with the sug- 
gestions given above, the nickel deposit is made 0.1 to 0.25 
millimeter thick, and the back, which is to be reinforced, 
cleansed with nitric acid and rinsed, and then as rapidly as 
possible brought into the copper bath to be reinforced to 2.5 
or 3 millimeters in thickness, the copper will adhere firmly 
and a durable matrix will be obtained. 

By means of galvanoplasty matrices of massive nickel or 
cobalt for use in the casting machine may even be produced. 
However, by reason of their hardness, such massive nickel 
matrices are justified with difficulty, and besides they are too 
expensive. 

While no experiments for the production of nickel matrices 
have been made with Weston's baths, nickel deposits several 
millimeters in thickness can without doubt be made with them 
by slightly changing their composition and heating them to 
between 176° and 194° F. In the experiments made baths of 
the composition given on p. 266 were used. They contained 
in 100 quarts, 77 lbs. of nickel sulphate and 39.6 lbs. of mag- 
nesium sulphate, and were always kept slightly acid with 
acetic acid, the temperature during deposition being as con- 
stantly as possible maintained at 194° F. 

The originals have to be prepared in a manner different 
from that for matrices in copper. In place of wax for insulat- 
ing the surfaces which are to receive no deposit, a material 
which does not soften at 194° F. has to be used. For this 
purpose, it was found most suitable to cast plaster of Paris 
around the original, or a paste of asbestos meal and water- 
glass. By treatment for 10 hours in the hot nickel bath dur- 
ing which time the current must in no wise be interrupted, 
and the original, especially in the beginning, be vigorously 



GALVANOPLASTY (REPRODUCTION). 667 

shaken, a nickel deposit about 0.25 millimeter in thickness is 
obtained. This deposit, as previously described, is reinforced 
iii the acid copper bath to about 1.75 to 2.25 millimeters in 
thickness, and zinc having in the usual manner been cast 
around it, is justified for the casting machine. 

The production of nickel matrices may also be effected with 
the use of the cold nickel bath described on p. 267, but much 
more time is required. In this case the originals may of course 
be insulated with wax. 

IV. Galvanoplasty in Silver and Gold. 

The preparation of reproductions in silver and gold pre- 
sents many difficulties. While copper is reducible in a com- 
pact state from its sulphate solution, silver and gold have to 
be reduced from their double salt solutions — potassium-silver 
cyanide and potassium-gold cyanide. However, these alka- 
line solutions attack moulds of fatty substances, such as wax 
and stearine, consequently also, plaster-of-Paris moulds im- 
pregnated with these substances, as well as gutta perch a and 
gelatine. Hence, only metallic moulds can be advantageously 
used, unless the end is to be attained in a round-about way ; 
that is, by first coating the mould with a thin film of copper, 
reinforcing this in the silver or gold bath, and finally dis- 
solving the film of copper with dilute nitric acid. 

The double salt solutions mentioned above require a well- 
conducting surface such as cannot be readily prepared by 
black-leading, a further reason why metallic moulds are to be 
preferred. 

The simplest way for the galvanoplastic reproduction in gold 
or silver of surfaces not in too high relief or too much under- 
cut, is to cover the object with lead, silver or gold foil, and 
pressing softened gutta-percha upon it. The foil yields to the 
pressure without tearing, and adheres to the gutta-percha so 
firmly that it can be readily separated together with it. This 
method is of course only applicable if the originals to be 
moulded can bear the pressure of the press. 



668 ELECTRO-DEPOSITION OF METALS. 

With originals which cannot stand pressure, or have portions 
in very high relief, or much undercut, oil gutta-percha may 
be used. The original secured to a brass plate, having been 
heated to between 122° and 140° F. and slightly oiled, the oil 
gutta-percha in small cubes is applied so that one cube is first 
placed upon the original, and, when soft, pressed firmly down 
with the moistened finger, other cubes being then in the same 
manner applied until the entire surface of the original is cov- 
ered, when the whole is allowed to cool, which may be accel- 
erated by placing it in very cold water. This impression can 
be detached in good shape from the original by the use of gen- 
tle force, the oil gutta-percha being in a hardened state suffi- 
ciently pliable to allow of its being readily taken out from the 
undercut portions. The face of the mould is next freed from 
oil by means of alcohol, or by brushing with liquid ammonia, 
and then dried. Now powder the mould with fine silver 
powder, thoroughly rubbing the latter with a brush into the 
depressions, so that it adheres firmly to the gutta-percha, and 
after blowing off an excess, bring the mould into the silver bath. 

The most suitable composition of the galvanoplastic silver 
bath is as follows : 

Fine silver (in the form of silver cyanide) If ozs., 99 per 
cent, potassium cyanide 4^ ozs., water 1 quart. 

Maximum current- density, 0.3 ampere. 

A slighter current-density than that given above can only 
be beneficial, and the electro-motive force should be as low as 
possible, the best deposits having been obtained with 0.5 volt 
and an electrode-distance of 10 centimeters. 

For galvanoplasty in gold, the same process as described 
above is used. Good results are obtained with a bath com- 
posed as follows : 

Fine gold (in the form of neutral chloride of gold or fulmi- 
nating gold) 1 oz., 99 per cent, potassium cyanide 3J ozs., 
water 1 quart. 

Current-density, 0.1 ampere. 

Electro-motive force at 10 cm. electrode-distance, 0.4 volt. 



CHAPTER XVIII. 

CHEMICALS USED IN ELECTRO-PLATING AND GALVANOPLASTY. 

Below the characteristic properties of the chemical prod- 
ucts employed in the workshop will be briefly discussed, 
and the reactions indicated which allow of their recognition. 
It frequently happens that the labels become detached from 
the bottles and boxes, thus rendering the determination of 
their contents necessary. 

I. Acids. 

1. Sulphuric acid (oil of vitriol). — Two varieties of this acid 
are found in commerce, viz.. fuming sulphuric acid (disul- 
phuric acid) and ordinary sulphuric acid. The first is a thick 
oily fluid, generally colored yellowish by organic substances. 
and emits dense, white vapors in the air. Its specific gravity 
is 1.87 to 1.89. The only purpose for which fuming sulphuric 
acid is used in the electroplating art, is as a mixture with 
nitric acid for stripping silvered objects. 

Ordinary sulphuric acid has a specific gravity of 1.84. 
Diluted with water it serves for filling the Bunsen elements 
and as a pickle for iron ; in a concentrated state it is used in 
the preparation of pickles and as an addition to the galvano- 
plastic copper bath. The crude commercial acid generally 
contains arsenic, hence care must be had to procure a pure 
article. In diluting the acid with water, it should in all cases 
be added to the water in a very gentle stream and with con- 
stant stirring, as otherwise a sudden generation of steam of 
explosive violence might result, and the dangerous corrosive 
liquid be scattered in all directions. Concentrated sulphuric 
acid vigorously attacks all organic substances, and hence has 

(669) 



670 ELECTRO-DEPOSITION OP METALS. 

to be kept in bottles with glass stoppers, and bringing it in 
contact with the skin should be carefully avoided. 

Recognition. — One part of the acid mixed with 25 parts of 
distilled water gives, when compounded with a few drops of 
barium chloride solution, a white precipitate of barium sul- 
phate. 

2. Nitric acid (aqua fortis, spirit of nitre). — It is found in 
trade of various degrees of strength. For our purposes, acid 
of 40° and 30° Be. is generally used. The acid is usually a 
more or less deep yellow, and frequently contains chlorine. 
The vapors emitted by nitric acid are poisonous and of a char- 
acteristic odor, by which the concentrated acid is readily dis- 
tinguished from other acids. It is used for filling the Bunsen 
elements (carbon in nitric acid), and for pickling in combina- 
tion with sulphuric acid and chlorine. On coming in contact 
with the skin it produces yellow stains. 

Recognition. — By heating the not too dilute acid with cop- 
per, brown-red vapors are evolved. For the determination of 
dilute nitric acid, add a few drops of it to green vitriol solu- 
tion, when a black-brown coloration will be produced on the 
point of contact. 

3. Hydrochloric acid (muriatic acid). — The pure acid is a 
colorless fluid which emits abundant fumes in contact with 
the air, and has a pungent odor by which it is readily dis- 
tinguished from other acids. The specific gravity of the 
strongest hydrochloric acid is 1.2. The crude acid of com- 
merce has a yellow color, due to iron, and contains arsenic. 
Dilute hydrochloric acid is used for pickling iron and zinc. 

Recognition. — On adding to the acid, very much diluted 
with distilled water, a few drops of solution of nitrate of silver 
in distilled water, a heavy white precipitate is formed, which 
becomes black by exposure to the light. 

4. Hydrocyanic acid (prussic acid). — This extremely poison- 
ous acid exists in nature only in a state of combination in 
certain vegetables and fruits, and especially in the kernels of 
the latter, as, for instance, in the peach, the berries of the 



CHEMICALS USED IN ELECTRO-PLATING. 671 

cherry laurel, bitter almonds, the stones of the apricot, of 
plums, cherries, etc. It may be obtained anhydrous, but in 
this state it is useless, and very difficult to preserve from de- 
composition. Diluted hydrocyanic acid is colorless, with a 
bitter taste and the characteristic smell of bitter almonds. It 
is employed in the preparation of gold immersion baths, and 
for the decomposition of the potassa in old silver baths. The 
inhalation of the vapors of this acid may have a fatal effect, 
as also its coming in contact with wounds. 

Recognition. — By its characteristic smell of bitter almonds. 
Or mix it with potash lye until blue litmus paper is no longer 
reddened, then add solution of green vitriol which has been 
partially oxidized by standing in the air, and acidulate with 
hydrochloric acid. A precipitate of Berlin blue is formed. 

5. Citric acid. — Clear colorless crystals of 1.542 specific 
gravity, which dissolve with great ease in both hot and cold 
water. It is frequently employed for acidulating nickel baths, 
and, combined with sodium citrate, in the preparation of plati- 
num baths. 

Recognition. — Lime-water compounded with aqueous solu- 
tion of citric acid remains clear in the cold, but on boiling 
deposits a precipitate of calcium citrate. The precipitate is 
soluble in ammonium chloride, but on boiling is again pre- 
cipitated, and is then insoluble in sal ammoniac. 

6. Boric acid (boracic acid). — This acid is found in commerce 
in the shape of scales with nacreous luster and greasy to the 
touch ; when obtained from solutions by evaporation, it forms 
colorless prisms. Its specific gravity is 1.435; it dissolves 
with difficulty in cold water (1 part of acid requiring at 
64.4° F. 28 of water), but is more rapidly soluble in boiling 
water (1 part of acid requiring 3 of water at 212° F.). Accord- 
ing to Weston's proposition, boric acid is employed as an 
addition to nickel baths, etc. 

Recognition. — By mixing solution of boric acid in water with 
some hydrochloric acid and dipping turmeric paper in the 
solution, the latter acquires a brown color, the color becoming 



672 ELECTRO-DEPOSITION OF METALS. 

more intense on drying. Alkalies impart to turmeric paper 
a similar coloration, which, however, disappears on immersing 
the paper in dilute hydrochloric acid. 

7. Arsenious acid (ivhite arsenic, arsenic, ratsbane). — It gen- 
erally occurs in the shape of a white powder, and sometimes 
in vitreous-like lumps, resembling porcelain. For our pur- 
poses the white powder is almost exclusively used. It is 
slightly soluble in cold water, and more readily so in hot water 
and hydrochloric acid. Notwithstanding its greater specific 
gravity (3.7), only a portion of the powder sinks to the bottom 
on mixing it with water, another portion being retained on 
the surface by air bubbles adhering to it. It is employed as 
an addition to brass baths, further, in the preparation of 
arsenic baths, for blacking copper alloys, and in certain 
silver whitening baths. 

Recognition. — When a small quantity of arsenious acid is 
thrown upon glowing coals an odor resembling that of garlic 
is perceptible. By mixing solution of arsenious acid, prepared 
by boiling with water, with a few drops of ammoniacal solu- 
tion of nitrate of silver, a yellow precipitate of arsenate of 
silver is obtained. The ammoniacal solution of nitrate of 
silver is prepared by adding ammonia to solution of nitrate of 
silver until the precipitate at first formed disappears. 

8. Chromic acid. — It forms crimson-red needles, and also 
occurs in commerce in the shape of a red powder. It is read- 
ily soluble in water, forming a red fluid, which serves for 
filling batteries. 

Recognition. — Chromic acid can scarcely be mistaken for 
any other chemical product employed by the electro-plater. 
A very much diluted solution of it gives, after neutralization 
with caustic alkali and adding a few drops of nitrate of silver 
solution, a crimson-red precipitate of chromate of silver. 

9. Hydrofluoric acid. — A colorless, corrosive, ver} r mobile 
liquid of a sharp, pungent odor. The anhydrous acid fumes 
strongly in the air and attracts moisture with avidity. Hydro- 
fluoric acid is used for etching glass and for pickling alumin- 



CHEMICALS USED IN ELECTRO-PLATING. 673 

ium dead white. Great care must be observed in working 
with the acid, since not only the aqueous solution, but also 
the vapors, have an extremely corrosive effect upon the skin 
and respiratory organs. 

Recognition. — By covering a small platinum dish containing 
hydrofluoric acid with a glass plate free from grease, the latter 
in half an hour appears etched. 

II. Alkalies and Alkaline Earths. 

10. Potassium hydrate {caustic potash). — It is found in com- 
merce in various degrees of purity, either in sticks or cakes. 
It is very deliquescent, and dissolves readily in water and 
alcohol ; by absorbing carbonic acid from the air it rapidly 
becomes converted into the carbonate, and thus loses its caustic 
properties. It should, therefore, be kept in well-closed vessels. 
Substances moistened with solution of caustic potash give rise 
to a peculiar soapy sensation of the skin when touched. It 
should never be allowed to enter the mouth, as even dilute 
solutions almost instantaneously remove the lining of tender 
skin. Should such an accident happen, the mouth should at 
once be rinsed several times with water and then with very 
dilute acetic acid. Pure caustic potash serves as an addition 
to zinc baths, gold baths, etc. For the purpose of freeing ob- 
jects from grease the more impure commercial article is used. 

11. Sodium hydrate (caustic soda). — It also occurs in com- 
merce in various degrees of purity, either in sticks or lumps. 
It is of a highly caustic character, resembling potassium 
hydrate (see above) in properties and effects. It is employed 
for freeing objects from grease, for the preparation of alkaline 
tin and zinc baths, etc. 

12. Ammonium hydrate (ammonia or spirits of hartshorn). — 
It is simply water saturated with ammonia gas. By exposure 
ammonia gas is gradually evolved, so that it must be kept in 
closely-stoppered bottles, in order to preserve the strength of 
the solution unimpaired. Four qualities are generally found 
in commerce, viz., ammonia of 0.910 specific gravity (contain- 

43 



674 ELECTRO-DEPOSITION OF METALS. 

ing 24.2 per cent, of ammonia gas) ; of 0.920 specific gravity 
(with 21.2 per cent, of ammonia gas); of 0.940 specific gravity 
(with 15.2 per cent, of ammonia gas); and 0.960 specific grav- 
ity (with 9.75 per cent, of ammonia gas). It is employed for 
neutralizing nickel and cobalt baths when too acid, in the 
preparation of fulminating gold, and as an addition to some 
copper and brass baths. 

Recognition. — By the odor. , 

13. Calcium, hydrate {burnt or quick lime). — It forms hard, 
white to gray pieces, which on moistening with water crumble 
to a light white powder, evolving thereby much heat. Vienna 
lime is burnt lime containing magnesia. Lime serves for free- 
ing objects from grease, and for this purpose is made into a 
thinly-fluid paste with chalk and water, with which the objects 
to be freed from grease are brushed. Vienna lime is much 
used as a polishing agent. 

III. Sulphur Combinations. 

14. Sulphuretted hydrogen (sulphydric acid, hydrosulphuric 
acid). — A very poisonous, colorless gas with a fetid smell re- 
sembling that of rotten eggs. Ignited in the air, it burns with 
a blue flame, sulphurous acid and water being formed. At the 
ordinary temperature water absorbs about three times its own 
volume of the gas, and then acquires the same properties as the 
gas itself. Sulphuretted hydrogen serves for the metallizing 
of moulds as described in the preceding chapter, where the 
manner of generating it is also given. It is sometimes em- 
ployed for the production of " oxidized " silver. Care should 
be taken not to bring metallic salts, gilt or silvered articles, or 
pure gold and silver in contact with sulphuretted hydrogen, 
they being rapidly sulphurized by it. 

Recognition. — By its penetrating smell ; further, by a strip of 
paper moistened with sugar of lead solution becoming black 
when brought into a solution of sulphuretted hydrogen or an 
atmosphere containing it. 

15. Potassium sulphide (liver of sulphur). — It forms a hard 



CHEMICALS USED IN ELECTRO-PLATING. 675 

green-yellow to pale-brown mass, with conchoidal fracture. It 
readily absorbs moisture, whereby it deliquesces and smells of 
sulphuretted hydrogen. It is employed for coloring copper 
and silver black. 

Recognition. — On pouring an acid over liver of sulphur, 
sulphuretted hydrogen is evolved with effervescence, sulphur 
being at the same time separated. 

16. Ammonium sulphide (sulphydrate or hydrosulphate of am- 
monia). — When freshly prepared it forms a clear and colorless 
fluid, with an odor of ammonia and sulphuretted hydrogen ; 
by standing it becomes yellow, and, later on, precipitates sul- 
phur. It is used for the same purpose as liver of sulphur. 

17. Carbon disulphide or bisulphide. — Pure carbon disulphide 
is a colorless and transparent liquid which is very dense, and 
exhibits the property of double refraction. Its smell is char- 
acteristic and most disgusting, and may be compared to that of 
rotten turnips. It burns with a blue flame of sulphurous acid, 
carbonic acid being at the same time produced. It is used as 
a solvent for phosphorus and rubber in metallizing moulds 
according to Parkes' method. This solution should be very 
carefully handled. 

18. Antimony sulphide. — a. Black sulphide of antimony (sti- 
bium sulfuratum nigrum) is found in commerce in heavy, gray 
and lusterless pieces or as a fine black-gray powder, with slight 
luster. It serves for the preparation of antimony baths, and 
for coloring copper alloys black. 

b. Red sulphide of antimony (stibium sulfuratum aurantia- 
cum) forms a delicate orange-red powder without taste or odor ; 
it is insoluble in water, but soluble in ammonium sulphide, 
spirits of hartshorn and alkaline lyes. In connection with 
ammonium sulphide or ammonia it serves for coloring brass 
brown. 

19. Arsenic trisulphide or arsenious sulphide (orpiment). — It 
is found in commerce in the natural, as well as artificial, state, 
the former occurring mostly in kidney-shaped masses of a 
lemon color, and the latter in more orange-red masses, or as a 



676 ELECTRO-DEPOSITION OF METALS. 

dull yellow powder. Specific gravity 3.46. It is soluble in 
the alkalies and spirits of sal ammoniac. 

20. Ferric sulphide. — Hard, black masses generally in flat 
plates, which are only used for the generation of sulphuretted 
hydrogen. 

IV. Chlorine Combinations. 

21. Sodium chloride (common salt, rock salt). — The pure salt 
should form white, cubical crystals, of which 100 parts of cold 
water dissolve 36, hot water dissolving slightly more. The 
specific gravity of sodium chloride is 2.2. In electroplating 
sodium chloride is employed as a conducting salt for some 
gold baths, as a constituent of argentiferous pastes, and for 
precipitating the silver as chloride from argentiferous solutions. 

Recognition. — An aqueous solution of sodium chloride on 
being mixed with a few drops of lunar caustic solution, yields 
a white caseous precipitate, which becomes black by exposure 
to light, and does not dissappear by the addition of nitric acid, 
but is dissolved by ammonia in excess. 

22. Ammonium chloride (sal ammoniac). — A white substance 
found in commerce in the shape of tough fibrous crystals. It 
has a sharp saline taste, and is soluble in 2J parts of cold, and 
in a much smaller quantity of hot water. By heat it is sub- 
limed without decomposition. It serves for soldering and 
tinning, and as a conducting salt for many baths. 

Recognition. — By sublimation on heating. By adding to a 
saturated solution of the salt a few drops of solution of platinum 
chloride, a yellow precipitate of platoso-ammonium chloride 
is formed. 

23. Antimony trichloride (butter of antimony). — A cr} 7 stalline 
mass which readily deliquesces in the air. Its solution in 
hydrochloric acid yields the liquor stibii chlorati, also called 
liquid butter of antimony. It has a yellowish color, and on 
mixing with water yields an abundant white precipitate, 
soluble in potash lye. The solution serves for coloring brass 
steel-gray, and for browning gun-barrels. 



CHEMICALS USED IN ELECTRO-PLATING. 677 

24. Arsenious chloride. — A thick, oily fluid, which evaporates 
in the air with the emission of white vapors. 

25. Copper chloride. — Blue-green crystals readily soluble in 
water. The concentrated solution is green, and the dilute 
solution blue. On evaporating to dryness, brown-yellow 
copper chloride is formed. It is employed in copper and 
brass baths as well as for patinizing. 

26. Tin chloride. — a. Stannous chloride or tin salt. A white 
crystalline salt readily soluble in water, but its solution on 
exposure to the air becomes turbid ; by adding, however, 
hydrochloric acid, it again becomes clear. On fusing the 
crystallized salt loses its water of crystallization, and forms a 
solid non-transparent mass of a pale yellow color — the fused 
tin salt. The crystallized, as well as the fused, salt serves for 
the preparation of brass, bronze and tin baths. 

Recognition. — By pouring hydrochloric acid over a small 
quantity of tin salt and adding potassium chromate solution, 
the solution acquires a green color. By mixing dilute tin 
salt solution with some chlorine water and adding a few drops 
of gold chloride solution, purple of Cassius is precipitated ; 
very dilute solutions acquire a purple color. 

b. Stannic chloride occurs in commerce in colorless crystals. 
In the anhydrous state it forms a yellowish, strongly fuming 
caustic liquid known as the "fuming liquor of Libadius." 

27. Zinc chloride {hydrochlorate or muriate of zinc ; butter of 
zinc). — A white crystalline or fused mass which is very solu- 
ble and deliquescent. The salt prepared by evaporation gen- 
erally contains some zinc oxychloride, and hence does not 
yield an entirely clear solution. It serves for preparing brass 
and zinc baths, and its solution in nickeling by immersion, 
soldering, etc. 

Recognition.— Solution of caustic potash separates a volumi- 
nous precipitate of zinc oxyhydrate, which redissolves in an 
excess of the caustic potash solution. By conducting sul- 
phuretted hydrogen into a solution of a zinc salt acidulated 
with acetic acid, a precipitate of white zinc sulphide is formed. 



678 ELECTRO-DEPOSITION OF METALS. 

28. Chloride of zinc and ammonia. — This salt is a combina- 
tion of zinc chloride and ammonium chloride, and forms very 
deliquescent crystals. Its solution in water serves for solder- 
ing, and zincking by contact. 

29. Nickel chloride. — It is found in commerce in the shape 
of deep green crystals and of a pale green powder. The latter 
contains considerably less water and less free acid than the 
crystallized article, and is to be preferred for electro-plating 
purposes. The crystallized salt dissolves readily in water, and 
the powder somewhat more slowly. Should the solution of the 
latter deposit a yellow precipitate, consisting of basic nickel 
chloride, it has to be brought into solution by the addition of 
a small quantity of hydrochloric acid. Nickel chloride is em- 
ployed for nickel baths. 

Recognition — By mixing the green solution of the salt with 
some spirits of sal ammoniac, a precipitate is formed, which 
dissolves in an excess of spirits of sal ammoniac, the solution 
showing a deep blue color. 

30. Cobaltous chloride. — It forms small rose-colored crystals, 
which, on heating, yield their water of crystallization, and are 
converted into a blue mass. The crystals are readily soluble 
in water, while the anhydrous blue powder dissolves slowly. 
Cobalt chloride is employed for the preparation of cobalt baths. 

Recognition. — Caustic potash precipitates from a solution of 
cobalt chloride a blue basic salt which is gradually converted 
into a rose-colored hydrate, and, with the access of air, into 
green-brown cobaltous hydrate. The aqueous solution yields 
with solution of yellow prussiate of potash, a pale gray-green 
precipitate. 

31. Silver chloride. — A heavy white powder which by ex- 
posure to light becomes gradually blue-gray, then violet, and 
finally black. When precipitated from silver solutions, a case- 
ous precipitate is separated. At 500° F. it fuses, without 
being decomposed, to a yellowish fluid which, on cooling, con- 
geals to a transparent, tenacious, horn-like mass. Silver 
chloride is practically insoluble in water, but dissolves with 



CHEMICALS USED IN ELECTRO-PLATING. 679 

ease in liquid ammonia and in potassium cyanide solution. 
It is employed in the preparation of baths for silver-plating, 
for silvering by boiling, and in the pastes for silvering by 
friction. 

Recognition. — By its solubility in ammonia, pulverulent 
metallic silver being separated from the solution by dipping 
in it bright ribands of copper. 

32. Gold chloride (terchloride of gold, muriate of gold, auric- 
chloride). — This salt occurs in commerce as crystallized gold 
chloride of an orange-yellow color, and as a brown crystalline 
mass which is designated as neutral gold chloride, or as gold 
chloride free from acid, while the crystallized articles always 
contains acid, and, hence, should not be used for gold baths. 
Gold chloride absorbs atmospheric moisture and becomes re- 
solved into a liquid of a fine gold color. On being moder- 
ately heated, yellowish-white aurous chloride is formed, and 
on being subjected to stronger heat, it is decomposed to me- 
tallic gold and chlorine gas. By mixing its aqueous solution 
with ammonia, a yellow-brown powder consisting of fulminat- 
ing gold is formed. In a dry state this powder is highly ex- 
plosive, and, hence, when precipitating it from gold chloride 
solution for the preparation of gold baths, it must be used 
while still moist. 

Recognition, — By the formation of the precipitate of fulmi- 
nating gold on mixing the gold chloride solution with ammo- 
nia. Further, by the precipitation of brown metallic gold 
powder on mixing the gold chloride solution with green vitriol 
solution. 

33. Platinic chloride. — The substance usually known by this 
name is hydroplatinic chloride. It forms red-brown, very 
soluble — and in fact deliquescent — crystals. With ammonium 
chloride it forms platoso-ammonium chloride. Both com- 
binations are used in the preparation of platinum baths. 
The solution of platinic chloride also serves for coloring silver, 
tin, brass and other metals. 

Recognition. — By the formation of a precipitate of yellow 



680 ELECTRO-DEPOSITION OF METALS. 

platoso-ammonium chloride on mixing concentrated platinie 
chloride solution with a few drops of saturated sal ammoniac 
solution. 

V. Cyanides. 

34. Potassium cyanide (white prussiate of potash). — For 
electro-plating purposes pure potassium cyanide with 98 to 
99 per cent., as well as that containing 80, 70 and 60 per 
cent., is used, whilst for pickling the preparation with 45 per 
cent, is employed. For the preparation of alkaline copper 
and brass baths, as well as silver baths, the pure 98 to 99 per 
cent, product is generally employed. However, for preparing 
gold baths the 60 per cent, article is mostly preferred, because 
the potash present in all potassium cyanide varieties with a 
lower content renders fresh baths more conductive. However, 
gold baths may also be prepared with 98 per cent, potassium 
cyanide without fear of injury to the efficiency of the baths, 
while, under ordinary circumstances, a preparation with less 
than 98 per cent, may safely be used for the rest of the baths. 
However, when potassium cyanide has to be added to the 
baths, as is from time to time necessary, only the pure pre- 
paration free from potash should be used, because the potash 
contained in the inferior qualities gradually thickens the bath 
too much. 

No product is more important to the electro-plater than 
potassium cyanide. The pure 98 to 99 per cent, product is a 
white, transparent, crystalline mass, the crystalline structure 
being plainly perceptible upon the fracture. In a dry state it 
is odorless, but when it has absorbed some moisture it has a 
strong smell of prussic acid. It is readily soluble in water, 
and should be dissolved in cold water only, since when poured 
into hot water it is partially decomposed, which is recognized 
by the appearance of an odor of ammonia. Potassium cyanide 
solution in cold water may, however, be boiled for a short 
time without suffering essential decomposition. Potassium 
cyanide must be kept in well-closed vessels, since when ex- 



CHEMICALS USED IN ELECTRO-PLATING. 681 

posed to the air it becomes deliquescent, and is decomposed 
b}' the carbonic acid of the air, whereby potassium carbonate 
is formed while prussic acid escapes. It is a deadly poison 
and must be used with the utmost caution. 

While pure fused potassium cyanide of 98 to 99 per cent, 
could formerly be everywhere obtained in commerce, the pres- 
ent commercial product consists, as a rule, of a mixture of 
potassium cyanide and sodium cyanide. The reason for this 
is that the dried yellow prussiate of potash was formerly fused 
by itself, whereby one-third of its content of cyanogen was 
lost, while, for the purpose of fixing this quantity of cyanogen, 
it is now fused with metallic sodium. The resultant product 
contains 78 per cent, potassium cyanide and 21 per cent, 
sodium cyanide. 

While for many electro-plating purposes, this mixture may 
take the place of pure potassium cyanide, its use for some pro- 
cesses, for instance, in the preparation of more concentrated 
gold baths, is connected with certain drawbacks. While the 
double salt — potassium-gold cyanide — dissolves very readily, 
sodium-gold cyanide is less soluble and separates in the form 
of a pale yellow powder. Sodium-copper cyanide shows a 
similar behavior, it being less soluble than the potassium 
double salt and as the electro-motive forces for decomposing 
the potassium and sodium double salts vary, the use of a mix- 
ture of potassium cyanide and sodium cyanide is, to say the 
least, not rational. For certain purposes the electro-plater 
should demand from his dealer pure potassium cyanide free 
from sodium cyanide. 

Potassium cyanide with 80, 70, 60 or 45 per cent, forms a 
gray-white to white mass with a porcelain-like fracture. A 
pale gray coloration is not a proof of impurities, being due to 
somewhat too high a temperature in fusing. These varieties 
are found in commerce in irregular lumps or in sticks, the 
use of the latter offering no advantage. Their behavior to- 
wards the air and in dissolving is the same as that of the pure 
product. 



682 



ELECTRO-DEPOSITION OF METALS. 



Recognition. — By the bitter almond smell of the solution. 
By mixing potassium cyanide solution with ferric chloride and 
then with hydrochloric acid until the latter strongly predom- 
inates, a precipitate of Berlin blue is formed. 

The pure salt free from potash does not effervesce on add- 
ing dilute acid, which is, however, the case with the inferior 
qualities. 

To facilitate the use of potassium cyanide with a different 
content than that given in a formula for preparing a bath, 
the following table is here given : 



Potassium cyanide with 



98 per cent. 



80 per cent. 70 per cent. 



60 per cent. 



45 per cent. 



By weight. 


By weight. 


By weight. 


By weight. 


By weight. 


1 part = 


1.2o0 parts 


= 1.40.0 parts 


= 1.660 parts 


= 2.180 parts. 


0.820 part = 


1 part 


— 1.143 parts 


= 1.333 parts 


= 1.780 parts. 


0.714 part = 


0.875 part 


= 1 part 


= 1.170 parts 


= 1.550 parts. 


0.615 part = 


0.740 part 


= 0.857 part 


= 1 part 


= 1.450 parts. 


0.460 part = 


0.562 part 


= 0.643 part 


= 0.750 part 


== 1 part. 



35. Copper cyanide. — There is a cuprous and a cupric cj^a- 
nide ; that used for electro-plating purposes being a mixture 
of both. It is a green-brown powder, which should not be 
entirely dried, since in the moist state it dissolves with greater 
ease in potassium cyanide than the dried product. 

It is chiefly used in the form of a double salt potassium- 
copper cyanide, i. e., a combination of copper cyanide with 
potassium cj^anide, in the preparation of copper, brass, tombac, 
and red gold baths. 

Recognition. — By evaporating a piece of copper cyanide the 
size of a pea, or its solutions, in hydrochloric acid, to dryness 
on a. water-bath, wherein care must be taken not to inhale the 
vapors, and dissolving the residue in water, a green-blue 
solution is obtained which acquires a deep blue color by the 
addition of ammonia in excess. 



CHEMICALS USED IN ELECTRO-PLATING. 683 

36. Zinc cyanide {hydrocyanate of zinc, prussiate of zinc). — A 
white powder insoluble in water, but soluble in potassium 
cyanide, ammonia and the alkaline sulphites. The fresher it 
is, the more readily it dissolves, the dried product dissolving 
with difficulty. Its solution in potassium cyanide forms 
potassium-zinc cyanide, which is used for brass baths. 

Recognition. — By evaporating zinc cyanide, or its solution, 
with an excess of hydrochloric acid on the water-bath, zinc 
chloride remains behind, which is recognized by the same re- 
action given under zinc chloride. 

37. Silver cyanide {prussiate or hydrocyanate of silver). — A 
white powder which slowly becomes black when exposed to 
light. It is insoluble in water and cold acids, which, how- 
ever, will dissolve it with the aid of heat. At 750° F. it melts 
to a dark red fluid, which, on cooling, forms a yellow mass 
with a granular structure. It is readily dissolved by potas- 
sium cyanide, but is only slightly soluble in ammonia, differ- 
ing in this respect from silver chloride. It forms a double 
salt with potassium cyanide — potassium-silver cyanide — and 
as such is employed in the preparation of silver baths. 

38. Potassium ferro-cyanide [yellow prussiate of potash). — It 
occurs in the shape of yellow semi-translucent crystals with 
mother-of-pearl luster, which break without noise. Exposed 
to heat they effloresce, losing their water of crystallization, and 
crumbling to a yellowish-white powder. For the solution of 
1 part of the salt, 4 of water of medium temperature are re- 
quired, the solution exhibiting a pale yellow color. It pre- 
cipitates nearly all the metallic salts from their solutions, 
some of the precipitates being soluble in an excess of the pre- 
cipitating agent. This salt is not poisonous. It serves for 
the preparation of silver and gold baths ; its employment, 
however, offering over potassium cyanide no advantages, 
unless the non-poisonous properties be considered as such. 

Recognition. — When the j'ellow solution is mixed with ferric 
chloride, a precipitate of Berlin blue is formed ; by blue vitriol 
solution a brown-red precipitate is obtained. 



(584 ELECTRO- DEPOSITION OF METALS. 

VI. Carbonates. 

39. Potassium carbonate (potash). — It is found in commerce 
in gray-white, bluish, yellowish pieces, the colorations being 
due to admixtures of small quantities of various metallic 
oxides. When pure it is in the form of a white powder, or in 
pieces the size of a pea. The salt, being very deliquescent, 
has to be kept in well-closed receptacles. It is readily soluble, 
and if pure, the solution in distilled water should be clear. It 
serves as an addition to some baths, and in an impure state 
for freeing objects from grease. 

Recognition. — The solution effervesces on the addition of 
hydrochloric acid. When neutralized with hydrochloric acid 
it gives with platinum chloride a heavy yellow precipitate of 
platinic potassium chloride, provided it be not too dilute. 

40. Acid potassium carbo'aate or monopotassic carbonate, com- 
monly called bicarbonate of potash. — Colorless, transparent, 
crystals, which at a medium temperature dissolve to a clear 
solution in 4 parts of water. It is not deliquescent; however, 
on boiling its solution it loses carbonic acid, and contains then 
only potassium carbonate. It is employed for the preparation 
of certain baths for gilding by simple immersion. 

41. Sodium carbonate (washing soda). — It occurs in commerce 
as crystallized or calcined soda of various degrees of purity. 
The crystallized product forms colorless crystals or masses of 
crystals, which, on exposure to air, rapidly effloresce and 
crumble to a white powder. By heating, the crystals also lose 
their water, a white powder, the so-called calcined soda, re- 
maining behind. Soda dissolves readily in water, and serves 
as an addition to copper and brass baths, for the preparation 
of metallic carbonates, and for freeing objects from grease, the 
ordinary impure soda being used for the latter purpose. 

The directions for additions of sodium carbonate to baths 
generally refer to the crystallized salt. If calcined soda is to 
be used instead, 0.4 part of it will have to be taken for 1 part 
of the crystallized product. 

42. Sodium bicarbonate {baking powder). — A dull white 



CHEMICALS USED IN ELECTRO-l'LATING. 685 

powder soluble in 10 parts of water of 68° F. On boiling, the 
solution loses one-half of its carbonic acid, and then contains 
sodium carbonate only. 

43. Calcium carbonate (marble, chalk). — When pure it forms 
a snow-white crystalline powder, a yellowish color indicating 
a content of iron. It is insoluble in water, but soluble, with 
effervescence, in hydrochloric, nitric and acetic acids. In 
nature, calcium carbonate occurs as marble, limestone, chalk. 

In the form of whiting (ground chalk carefully freed from 
all stony matter) it is used for the removal of an excess of 
acid in acid copper baths, and mixed with burnt lime, as an 
agent for freeing objects from grease. 

44. Copper carbonate. — Occurs in nature as malachite and 
allied minerals. The artificial carbonate is an azure-blue 
substance, insoluble in water, but soluble, with effervescence, 
in acids. Copper carbonate precipitated from copper solution 
by alkaline carbonates has a greenish color. Copper carbonate 
is employed for copper and brass baths and for the removal of 
an excess of acid in acid copper baths. 

Recognition. — Dissolves in acids with effervescence ; on dip- 
ping a ribband of bright sheet-iron in the solution, copper 
separates upon the iron. On compounding the solution with 
ammonia in excess, a deep blue coloration is obtained. 

45. Zinc carbonate. — A white powder, insoluble in water. 
The product obtained by precipitating a zinc salt with alka- 
line carbonate is a combination of zinc carbonate with zinc 
oxyhydrate. It serves for brass baths in connection with 
potassium cyanide. 

Recognition. — In a solution in hydrochloric acid, which is 
formed with effervescence, according to the reactions given 
under zinc chloride (27). 

46. Nickel carbonate. — A pale apple-green powder, insoluble 
in water, but soluble, with effervescence, in acids. It is em- 
ployed for neutralizing nickel baths which have become acid. 

Recognition. — In hydrochloric acid, it dissolves, with effer- 
vescence, to a green fluid. By the addition of a small quan- 



686 ELECTRO-DEPOSITION OF METALS. 

tity of ammonia, nickel oxyhydrate is precipitated, which, by 
adding ammonia in excess, is redissolved, the solution showing 
a blue color. 

47. Cobaltous carbonate. — A reddish powder, insoluble in 
water, but soluble in acids, the solution forming a red fluid. 

VII. Sulphates and sulphites. 

48. Sodium sulphate (Glauber's salt). — Clear crystals of a 
slightly bitter taste, which effloresce by exposure to the air. 
They are readily soluble in water. On heating, the crystals 
melt in their water of crystallization, and when subjected to a 
red heat, calcined Glauber's salt remains behind. It is used 
as an addition to some baths. 

49. Ammonium sulphate. — It forms a neutral, colorless salt, 
which is constant in the air, readily dissolves in water, and 
evaporates on heating. It serves as a conducting salt for 
nickel, cobalt and zinc baths. 

Recognition. — By its evaporating on heating. A concen- 
trated solution compounded with platinic chloride gives a 
yellow precipitate of platoso-ammonium chloride, while a 
solution mixed with a few drops of hydrochloric acid gives 
with barium chloride a precipitate of barium sulphate. 

50. Potassium-aluminium sulphate (potash-alum). — Colorless 
crystals or pieces of crystals with an astringent taste. It is 
soluble in water, 12 parts of it dissolving in 100 parts of water 
at the ordinary temperature. On heating, the crystals melt, 
and are converted into a white, spongy mass, the so-called 
burnt alum. Potash-alum serves for the preparation of zinc 
baths and for brightening the color of gold. 

Recognition. — On adding sodium phosphate to the solution 
of this salt a jelly-like precipitate of aluminium phosphate is 
formed, which is soluble in caustic potash, but insoluble in 
acetic acid. 

51. Ammonium-alum is exactly analogous to the above, the 
potassium sulphate being simply replaced by ammonium sul- 
phate. It is for most purposes interchangeable with potash- 



CHEMICALS USED IN ELECTRO-PLATING. 687 

* 

alum. On exposing ammonium-alum to a red heat, the am- 
monium sulphate is lost, pure alumina remaining behind. 
Ammonium-alum is used for preparing a bath for zincking 
iron and steel by immersion. 

Recognition. — The same as potash-alum. On heating the 
comminuted ammonium-alum with potash-lye, an odor of 
ammonia becomes perceptible. 

52. Ferrous sulphate (sulphate of iron, protosulphate of iron, 
copperas, green vitriol). — Pure ferrous sulphate forms bluish- 
green, transparent crystals of a sweetish, astringent taste, which 
readily dissolve in water, and effloresce and oxidize in the air. 
The crude article forms green fragments frequently coated 
with a yellow powder. It generally contains, besides ferrous 
sulphate, the sulphate of copper and of zinc, as well as ferric 
sulphate. Ferrous sulphate is employed in the preparation 
of iron baths, and for the reduction of gold from its solutions. 

Recognition. — By compounding the green solution with a 
few drops of concentrated nitric acid, a black-blue ring is 
formed on the point of contact. On mixing the lukewarm 
solution with gold chloride, gold is separated as a brown 
powder, which hy rubbing acquires the luster of gold. 

53. Iron-ammonium sulphate. — Green crystals which are 
constant in the air and do not oxidize as readily as green 
vitriol. 100 parts of water dissolve 16 parts of this salt. It 
is used for the same purposes as green vitriol. 

54. Copper sulphate (cupric sulphate, blue vitriol, or blue cop- 
peras). — It forms large, blue crystals, of which 190 parts of 
cold water dissolve about forty parts, and the same volume of 
hot water about 200 parts. Blue vitriol which does not pos- 
sess a pure blue color but shows a greenish luster, is contam- 
inated with green vitriol, and should not be used for electro- 
plating purposes. Blue vitriol serves for the preparation of 
alkaline copper and brass baths, acid copper baths, etc. 

Recognition. — By its appearance, as it can scarcely be mis- 
taken for anything else. A content of iron is recognized by 
boiling blue vitriol solution with a small quantity of nitric 



688 ELECTRO-DEPOSITION OF METALS. 

acid, and adding ammonia in excess ; brown flakes indicate 
iron. 

55. Zinc sulphate [white vitriol). — It forms small colorless 
prisms of a harsh metallic taste, which readily oxidize on ex- 
posure to the air. By heating the crystals melt, and by heat- 
ing to a red heat they are decomposed into sulphurous acid 
and oxygen, which escape, while zinc oxide remains behind as 
residue. 100 parts of water dissolve about 50 parts of zinc 
sulphate in the cold, and nearly 100 parts at the boiling- 
point. Zinc sulphate is employed for the preparation of brass 
and zinc baths, as well as for mat pickling. 

Recognition. — By mixing zinc sulphate solution with acetic 
acid and conducting sulphuretted hydrogen into the mixture, a 
white precipitate of zinc sulphide is formed. A slight content 
of iron is recognized by the zinc sulphate solution, made alka- 
line b} 7 ammonia, giving with ammonia sulphide a somewhat 
colored precipitate instead of a pure white one. However, a 
slight content of iron does no harm. 

56. Nickel sulphate. — Beautiful dark green crystals, readily 
soluble in water, the solution exhibiting a green color. On 
heating the crystals to above 536° F., yellow anhydrous nickel 
sulphate remains behind. Like the double salt described be- 
low, it serves for the preparation of nickel baths and for color- 
ing zinc. 

Recognition. — By compounding the solution with ammonia 
the green color passes into blue. Potassium carbonate pre- 
cipitates pale green basic nickel carbonate, which dissolves on 
adding ammonia in excess, the solution showing a blue color. 
A content of copper is recognized by the separation of black- 
brown copper sulphide on introducing sulphuretted hydrogen 
into a heated solution previously strongly acidulated with 
hydrochloric acid. 

57. Nickel-ammonium sulphate. — It forms green crystals of a 
somewhat paler color than nickel sulphate. This salt dissolves 
with more difficulty than the preceding, 100 parts of water 
dissolving only 5.5 parts of it. It is used for the same pur- 



CHEMICALS USED IN ELECTRO-PLATING. 689 

poses as the nickel sulphate, and is also recognized in the same 
manner. The following reaction serves for distinguishing it 
from nickel sulphate: By heating nickel' sulphate in concen- 
trated solution with the same volume of strong potash or soda 
lye, no odor of ammonia is perceptible, while nickel-ammon- 
ium sulphate evolves ammoniacal gas which forms dense 
clouds on a glass rod moistened with hydrochloric acid. 

58. Cobaltous sulphate. — Crimson crystals of a sharp metallic 
taste. They are constant in the air and readily dissolve in 
water, the solution showing a red color. By heating the 
crystals lose their water of crystallization without, however, 
melting, and become thereby transparent and rose-colored. 
The salt is used for cobalt baths for the electro-deposition of 
cobalt and for cobalting by contact. 

Recognition. — In the presence of ammoniacal salts, caustic 
potash precipitates a blue basic salt, which on heating changes 
to a rose-colored hydrate and, by standing for some time in 
the air, to a green-brown hydrate. By mixing a concentrated 
solution of the salt strongly acidulated with hydrochloric acid, 
with solution of potassium nitrate, a reddish-yellow precipitate 
is formed. 

59. Co bait- ammonium sulphate. — This salt forms crystals of 
the same color as cobalt sulphate, which, however, dissolve 
more readily in water. 

60. Sodium sulphite and bisulphite. — a. Sodium sulphite. 
Clear, colorless, and odorless crystals, which are rapidly trans- 
formed into an amorphous powder by efflorescence. The salt 
readily dissolves in water, the solution showing a slight alka- 
line reaction due to a small content of sodium carbonate. It 
is employed in the preparation of gold, brass, and copper baths, 
for silvering by immersion, etc. 

Recognition. — The solution when mixed with dilute sul- 
phuric acid has an odor of burning sulphur. 

b. Sodium bisulphite. — Small crystals, or more frequently 
in the shape of a pale yellow powder with a strong odor of sul- 
phurous acid and readily soluble in water. The solution 
44 



690 ELECTRO-DEPOSITION OP METALS. 

shows a strong acid reaction and loses sulphurous acid in the 
air. It is employed in the preparation of alkaline copper and 
brass baths. 

Both the sulphite and bisulphite must be kept in well- 
closed receptacles, as by the absorption of atmospheric oxygen 
they are converted to sulphate. 

61. Cuprous sulphite. — A brownish-red crystalline powder 
formed by treating cuprous hydrate with sulphurous acid solu- 
tion. It is insoluble in water, but readily soluble in potassium 
cyanide, with only slight evolution of cyanogen. It serves for 
the preparation of alkaline copper baths in place of basic ace- 
tate of copper (verdigris), blue vitriol, or cuprous oxide. 

VIII. Nitrates. 

62. Potassium nitrate (saltpetre, nitre). — It forms large, pris- 
matic crystals, generally hollow, but also occurs in commerce 
in the form of a coarse powder, soluble in 4 parts of water at a 
medium temperature. The solution has a bitter, saline taste 
and shows a neutral reaction. Potassium nitrate melts at a 
red heat, and on cooling congeals to an opaque, crystalline 
mass. It is employed in the preparation of desilvering pickle 
and for producing a mat luster upon gold and gilding. For 
these purposes it may, however, be replaced b}' the cheaper 
sodium nitrate, sometimes called cubic, nitre or Chile saltpetre. 

Recognition. — A small piece of coal when thrown upon melt- 
ing saltpetre burns fiercely. When a not too dilute solution 
of saltpetre is compounded with solution of potassium bitar- 
trate saturated at the ordinary temperature, a crystalline pre- 
cipitate of tartar is formed. 

63. Sodium nitrate (cubic nitre or Chile saltpetre). — Colorless 
crystals, deliquescent and very soluble in water ; the solution 
shows a neutral reaction. It is used for the same purposes as 
potassium nitrate. 

64. Mercurous nitrate. — It forms small, colorless crystals, 
which are quite transparent and slightly effloresce in the air. 
On heating, they melt and are transformed, with the evolution 



CHEMICALS USED IN ELECTRO-PLATING. 691 

of yellow-red vapors, into yellow-red mercuric oxide, which, 
on further heating, entirely evaporates. With a small quan- 
tity of water, mercurous nitrate yields a clear solution. By 
the further addition of water it shows a milky turbidity, 
which, however, disappears on adding nitric acid. It is em- \ 
ployed for quicking the zincs of the cells, and the objects 
previous to silvering, and for brightening (with subsequent 
heating) gilding. For the same purpose is also used : 

65. Mercuric nitrate (nitrate of mercury). — This salt is ob- 
tained with difficulty in a crystallized form. It is generally 
sold in the form of an oily, colorless liquid which, in contact 
with water, separates a basic salt. This precipitate disappears 
upon the addition of a few drops of nitric acid, and the liquid 
becomes clear. 

Recognition. — A bright ribband of copper dipped in solution 
of mercurous or mercuric nitrate becomes coated with a white 
amalgam, which disappears upon heating. 

66. Silver nitrate (lunar caustic). — This salt is found in com- 
merce in three forms : Either as crystallized nitrate of silver 
in thin, rhombic, and transparent plates ; or in amorphous, 
opaque, and white plates of fused nitrate ; or in small cylinders 
of a white, or gra}^ or black color, according to the nature of 
the mould employed, in which form it constitutes the lunar 
caustic for surgical uses. For our purposes only the pure, 
crystallized product, free from acid, should be employed. The 
crystals dissolve readily in water. In making solutions of this 
and other silver salts, only distilled water should be used ; all 
other waters, owing to the presence of chlorine, produce a 
cloudiness or even a distinct precipitate of silver chloride. 
When subjected to heat the crystals melt to a colorless, oily 
fluid, which, on cooling, congeals to a crystalline mass. Silver 
nitrate is employed in the preparation of chloride and cyanide 
of silver for silver baths. The solution in potassium cyanide 
may also be used for silver baths. The alcoholic solution is 
employed for metallizing non-conductive moulds for galvan- 
oplastic deposits. 



692 ELECTRO-DEPOSITION OF METALS. 

Recognition. — Hydrochloric acid and common salt solution 
precipitate from silver nitrate solution silver chloride, which 
becomes black on exposure to the light, and is soluble in am- 
monia. 

IX. Phosphates and Pyrophosphates. 

67. Sodium Phosphate. — Large, clear crystals, which readily 
effloresce, and whose solution in water shows an alkaline re- 
action. It is employed in the preparation of gold baths and 
for the production of metallic phosphates for soldering. 

Recognition. — The dilute solution compounded with silver 
nitrate yields a yellow precipitate of silver phosphate. 

68. Sodium pyrophosphate. — It forms white crystals, which 
are not subject to efflorescence, and are soluble in 6 parts of 
water at a medium temperature ; the solution shows an alka- 
line reaction. Sodium pyrophosphate also occurs in com- 
merce in the form of an anhydrous white powder, though it 
may here be said that the directions for preparing baths refer 
to the crystallized salt. It is employed in the preparation of 
gold, nickel, bronze, and tin baths. 

Recognition. — The dilute solution compounded with silver 
nitrate yields a white instead of a yellow precipitate. 

69. Ammonium phosphate. — A colorless crystalline powder 
quite readily soluble in water ; the solution should be as 
neutral as possible. A salt smelling of ammonia, as well as 
one showing an acid reaction, should be rejected. It is em- 
ployed in the preparation of platinum baths. 

X. Sails of Organic Acids. 

70. Potassium bitartrate {cream of tartar). — The pure salt 
forms small transparent crystals, which have an acid taste, 
and are slightly soluble in water. The commercial crude 
tartar or argol, which is a by-product in the wine-industry, 
forms gray or dirty -red crystalline crusts. In a finely pow- 
dered state, purified tartar is called cream of tartar. It is 
employed for the preparation of the whitening silver baths, 



CHEMICALS USED IN ELECTRO-PLATING. 693 

for those of tin, and for the silvering paste for silvering by 
friction, and in scratch-brushing different deposits. 

71. Potassium-sodium tartrate (Roclielle or Seigneite salt). — 
Clear colorless crystals, constant in the air. of a cooling, bitter, 
saline taste, and soluble in 2.5 parts of water of a medium 
temperature. The solution shows a neutral reaction. This 
salt is employed in the preparation of copper baths free from 
cyanide, as well as of nickel and cobalt baths, which are to be 
decomposed in the single cell apparatus. 

Recognition. — By the addition of acetic acid the solution 
yields an abundant precipitate of tartar. 

72. Antimony-potassium tartrate (tartar emetic). — A white 
crystalline substance, of which 100 parts of cold water dissolve 
5 parts, while a like volume of hot water dissolves 50 parts. 
The solution shows a slight acid reaction. The only use of 
this salt is for the preparation of antimony baths. 

Recognition. — The solution of the salt compounded with sul- 
phuric, nitric, or oxalic acid yields a white precipitate, in- 
soluble in an excess of the cold acid. Sulphuretted hydrogen 
imparts to the dilute solution a red color. Hydrochloric acid 
effects a precipitate, which is redissolved by the acid in excess. 

73. Copper acetate (verdigris). — It is found in the market in 
the form of dark green crystals showing an acid reaction, or 
as a neutral bright green powder. 

The crystallized copper acetate forms opaque dark green 
prisms, which readily effloresce, becoming thereby coated with 
a pale green powder. They dissolve with difficulty in water, 
but readily in ammonia, forming a solution of a blue color. 
They dissolve readily also in potassium cyanide and alkaline 
sulphites. 

The neutral copper acetate forms a blue-green crystalline 
powder, imperfectly soluble in water, but readily soluble in 
ammonia, forming a solution of a blue color. 

Copper acetate is used for preparing copper and brass baths, 
for the production of artificial patinas, for coloring, gilding, etc. 

Recognition. — On pouring sulphuric acid over copper ace- 



694 ELECTRO-DEPOSITION OF METALS. 

tate, a strong odor of acetic acid is noticed ; with ammonia it 
yields a blue solution. 

74. Lead acetate (sugar of lead). — Colorless lustrous prisms 
or needles of a nauseous sweet taste, and poisonous. The 
crystals effloresce in the air, melt at 104° F., and are readily 
soluble in water, yielding a slightly turbid solution. Lead 
acetate is employed for preparing lead baths (Nobili's rings) 
and for coloring copper and brass. 

Recognition. — By compounding lead acetate solution with 
potassium chromate solution, a heavy yellow precipitate of 
lead chromate is formed. 

75. Sodium citrate. — Colorless crystals, presenting a moist 
appearance, which are readily soluble in water ; the solution 
should show a neutral reaction. This salt is employed in the 
preparation of the platinum bath according to Bottger's for- 
mula, and as conducting salt for nickel and zinc baths. 



APPENDIX. 

Contents of Vessels. 

To find the number of gallons a tank or other vessel will 
hold, divide the number of cubic inches it contains by 231. 

If rectangular, multiply together the length, breadth and 
depth. 

If cylindrical, multiply the square of the diameter by 
0.7854, and the product by the depth. 

If conical, add together squares of diameters of top and 
bottom, and the product of the two diameters. Multiply their 
sum by 0.7854, and the resulting product by the depth. 
Divide the product by 3. 

If hemispherical, to three times the square of the radius at 
top add the square of the depth. Multiply this sum by the 
depth and the product- by 0.5236. 





Avoirdupois Weight. 








= Ounces. 


= Drams. 


= Grains. 


= Grams. 


1 Pound ...•".. 

1 Ounce 

1 Dram 


16 
1 
0.062 


256 

16 

1 


7,000 
437.5 
27.34 


453.25 

28.33 

1.77 





Troy 


Weight. 








= Ounces. 


= Dwt. 


= Grains. 


= Grams. 


1 Pound 

1 Ounce 

1 Pennyweight .... 


12 
1 
0.05 


240 

20 

1 


5,760 

480 
24 


372.96 

31.08 

1.55 



(695) 



696 



APPENDIX. 

Imperial Fluid Measure. 



i Gallon 

i Quart 

I Pint 

i Fluid Ounce . . . 
i Fluid Dram . . . 
i Minim 



£ 




CO 

-0 








a 




3 a 


II 


Ph 
li 


EtrO 

II 


4 


8 


160 


i 


2- 


40 


0.5 


I 


20 


0.025 


O.O5 


1 


0.0031 


O.O062 


0.125 


0.00005 


0.0001 


0.0021 



■26 
is 



1280 
320 
160 



0.0167 



76,800 

j 19,200 

9,600 

480 

60 

1 



_g 












II 


u 

II 


II 


70,000 


277.276 


4-541 


17,5°° 


69 310 


I-I35 


8,75° 


34-659 


0.567 


437-5 


1-733 


0.0284 


54-7 


0.217 


0.0035 


0.91 


0.0036 


0.00006 



•s-I 

U o 



4.541 

I.I35-2 

576.6 

283.8 

35-5 

0.59 



Table of Useful Numerical Data. 



•03937 


inches 


•3937° 


" 


3-937°o 


" 


39.37000 


" 


1 


gram. 


1000 


a 


1 ounces by 

315.271; y 

*>J 1 J I measure. 



1 millimeter equals 
1 centimeter " 
1 decimeter " 
1 meter " 

1 cubic centimeter of 

water equals 
1 liter " 

1 liter " 1 

1 gallon ( or 1 60 fluid \ , 

ounces) equals J 

1 gallon " 277.276 cubic ins 

1 pint (or 20 fluid 1 - .. 

> 34-659 " 
ounces equals J 

1 fluid ounce " 1-733 " 

1 liter " 61.024 " 

I avoirdupois pound 

equals 



f 



liters. 



7000. 



grains. 



1 troy pound equals 
1 avoirdupois ounce "> 

equals J 

I troy ounce equals 
1 avoirdupois drm. ) 

equals J 

1 troy pennyweight "1 

equals 
1 gram equals 
I kilogram equals 
1 liter of water equals 
1 cubic inch of water ) 

equals J 

I cubic centimeter of \ 

water equals > 
1 kilogram equals 



5760. grains. 

437-5 

480. " 

27-34 " 

24. " 

'5-43 " 
15432. 
15432. 

252.5 



35.274 avoir- 
dupois ozs 



To convert Fahrenheit thermometer degrees (F.) to Centigrade degrees (C), first 
subtract 32, then multiply by 5, and divide by 9. 

r - 5(F-- 32) 
9 

To convert Centigrade degrees to Fahrenheit degrees, multiply by 9, divide by 5, 
then add 32. 



9 C 



+ 32 



APPENDIX. 



697 



0) mvo O rovO 



i t-~ o cm ^t-vo (J\ i 



O e 3 n 



t-OO rOvO O « vo 



*\0 00 H 



i tj-vo r^. on o cm m in o vo 



ro -<j-\0 l>. ON O CM 



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i oo rooo --a-co cm t-N m 



273 S 
Og.6 



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rt- on -*■ on < 



Of Pints 
equals 
Cubic 
Inches. 


t^ >*■ O. -^-oo 


ro o>^o ro o-vo «oo -<*■ 10 w 1-^ ro 000 r~vo 
ro r^ n nmvo ro cy>MD w 0*0 n cm/in r-^ ro 
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ffiNd r>. w vo ro owo cm m 
t-. -*■ i— h t*- o> roco mvo 
m cm N cm ro rovo o rfiNt 

t-t H H CO 


Of Cubic 
Inches 
equals 
Pints. 


o 

o 


o 
o 


O O H 

ooo 


-*• r-* rovD ONCO t-^ 

M M N (N « <N lOOO 
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s 


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tJ-mn onco r^, in ^- cm in 
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H H CM CM CM CM mOO W tJ-00 


Of Liters 
equals 
Gallons. 


o 


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-<*-VO 00 
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ooo 


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H M H K M « -3"VO 00 


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H H H H 1-1 CM -^-VO OO 


w ro in t** cm -*t-vo 00 

H H H H H CM -<**vO OO H CM 


f Gallons 
als Liters. 





s 


.gog 
1.363 
1. 817 
2.272 
2.726 
3.180 
3-635 
4.089 
4-543 
9.087 
13.630 


t>» 


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CM NH\0 O inOvO m t*>TT 

cm cm roro-^-Tj-osrooocM in 











lo 


x> 


3 




U 


s 




-C 




c 
u 
U 


rt 




O 


3 

0- 






J2 






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H 


-u 


rr 






3 


V 






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d 







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>VO CMCO "^-i-t SfOCMOH 

o h w o fomt + invo 
0000000000 



■*■ w cm ro tj- invo i>-oo o\ o o O 



> tj- -^ invo cm 00 -«±- 



• ro 1 



) 0> t-svo "^- ( 



O O t^vo 



I CO 



> OOO CO f>.vO 



cm o^ in m 00 -^- m t^roo-M mo\ror**o "^-co t>-in-^roi-i ooo moh Nn o> o 
ro -^-vo 00 o h co ^vo cm om/ihco ^ m n rri s h inoSrot^.o" ^-Ci " 

on in w 00 -^- h t^. ( . 

1 "<l-vO CO ON m CO -*-vO 



1 "*vO CO ON m 



) -^-vo 



■ H NfONH in ONCO 

on in m ro 
) -tvOC 






i 3 4> 

! erg 



5(5 



c-s in m 

Cs. in H SO CM 


inomoinoooo 
t^s coco tonne in 


OoooOwMCMCMroTi-'4-in invo 
inomoinoooooooooo 


CM 00 Th 




SOnO CM roiOHvO CM 
M M M H CO "^-VO 


(n. roco ^-ONino inomo mo mo 
NONO CM COmHVO CM t>. roco i- om 


00000 
O m m 



1 -*vO r-OiO 



3 v a a 
cr ^ 3 c; 



rpvo ro onnd cm on m h 00 tJ- on moo mr-»cMvo wmo mMvo wvo hvo m ro -<t-vo t^ -<j- 
SS« SS r?J?5"^ 30^5 w ONmcMco mMco t|-o roco cm nhvo o m o mo in m 
OOOOOOOOOOOMHCMroroThin mvo cm ONmcvco mMoo ■^t-ON moo « m 

h m cm m m -<i- ut mvo « on in cm* •**- 
m h cm mvo 






O 



2g^ 

S3S 



2J "3"°5 N ^ ° '*" ° •-* m on onoo tN. t^-vo mm^rfSH moNCMvo o ror-*-<i-HoomM 

S 2 9 £ S 5i S Si fnfnmr^wmONmo»M m c^oo co t^vo vo m m **• m t^ w Ttoo c>» 

q o o o o o q o q o m h w r^ n m co m r-. m m on m t^ m m ooo co S\o m 
. HHMNCMrommr*»MinoNO\ 

°J "? W . ^ " *\* N . °°. ^ °? "* °° « NO O ^-00 CMVO0 OOOO ONONO»ON ONCO CO SSrh 

mcm int-sOeM 10 is d «' in 6 vd h" n« n moo* -<*-oo* cm'vo" mtNrt iAonononononon 

HMMMCMCM«mt^OCMmrN,ocMmovOHtNCM t^. moo conh m on on 

HHMM«CMCMinrN.ocMinrN.ocMinovOw\om 

q h i cm m *■*• mvo r^oo on o 

m cm m ■*■ mvo tN.oo oooooooooooooooo 

m cm m •»*■ mvo tN-oo o o o o o o o 

h cm ro --*- m o 



698 



APPENDIX. 



From the above table any ordinary conversions up to 2000 units may be readily 
made. For example : It is required to find the number of cubic centimeters equal 
to 1728 cubic inches. 

1728 = 1000 + 700 -)- 20 + 8 cubic inches. 
But a reference to the sixth column shows that 

1000 cubic inches = 16,385.92 cubic centimeters. 



700 


K 


= 11,470.10 


20 


if 


= 32772 


8 


« 


= i3*-°9 



Add together, and 1728 



28,314.83 



Table of Solubilities of Chemical Compounds Commonly Used in 
Electro- Technics 



Names. 



Acid potassium carbonate (bicarbonate of 
potash 

Aluminium chloride 

Aluminium sulphate (calculated to anhydrous 
salt) 

Ammonium alum - 

Ammonium chloride 

Ammonium sulphate 

Antimony potassium tartrate (tartar emetic) • • 

Arsenious acid •. 

Boric acid 

Cadmium chloride, crystallized 

Cadmium sulphate 

Chromic acid 

Citric acid 

Cobalt-ammonium sulphate (calculated to an- 
hydrous salt) 

Cobalt sulphate (calculated to anhydrous salt) 

Copper acetate (verdigris) neutral 

Copper chloride 

Copper sulphate ( blue vitriol) crystallized . . . 

Ferrous sulphate (green vitriol, copperas).. .. 

Gold chloride 

Gold cyanide 

Lead acetate (sugar of lead) 

Lead nitrate 

Magnesium sulphate (Epsom salt) 

Mercuric chloride (corrosive sublimate) 

Mercuric nitrate 

Mercuric sulphate 



Soluble in 100 parts by weight of 
water at 



50° F. 


212° F. 


Parts by weight. 


Parts by weight. 


23 


45 at 158° F. 


400 


very soluble. 


35 


1 130 


9 


422 


33 


73 


73-6 


97-5 


5- 2 


28 at 167 F. 


4 


9-5 


2.7 


29 


140 


149 


95 


80 


very soluble 


very soluble. 


133 


very soluble. 


11.6 


43.3 at 167 F. 


30.5 


63.7 at 158 F. 


7-4 


20 


soluble 


very soluble. 


37 


203 


61 


333 


soluble 


soluble. 


very soluble 


very soluble. 


45-35 


very soluble. 


48 


139 


3i-5 


71-5 


6-57 


54 


decomposable 


decomposable. 


decomposable 


decomposable. 



APPENDIX. 



699 



Table oj Solubilities of Chemical Compounds Commonly Used in 
Electro- Technics. — Continued. 



Names. 



Mercurous nitrate 

Mercurous sulphate 

Nickel-ammonium sulphate (calculated to an- 
hydrous salt) 

Nickel chloride, crystallized 

Nickel nitrate, crystallized 

Nickel sulphate (calculated to anhydrous 
salt) 

Platinic chloride 

Platoso-ammonium chloride 

Potassium-aluminium sulphate (potash alum), 
crystallized 

Potassium bitartrate (cream of tartar) 

Potassium carbonate (potash) 

Potassium-copper cyanide 

Potassium cyanide 

Potassium dicbromate 

Potassium ferrocyanide (yellow prussiate of 
potash) 

Potassium-gold cyanide 

Potassium nitrate (saltpetre) 

Potassium permanganate 

Potassium-silver cyanide 

Potassium-sodium tartrate (Rochelle or Seig- 
nette salt) 

Potassium sulphide (liver of sulphur) 

Potassium-zinc cyanide 

Silver nitrate (lunar caustic) < 

Sodium bisulphite 

Sodium carbonate, anhydrous (calcined soda) 

Sodium carbonate (crystallized soda) 

Sodium chloride (common salt) 

Sodium dichromate 

Sodium hydrate (caustic soda) 

Sodium hyposulphite, sodium thiosulphate 

(anhydrous salt) 

Sodium phosphate 

Sodium pyrophosphate 

Sodium sulphate (Glauber's salt) 

Sodium sulphite (neutral), crystallized 

Stannic chloride 

Stannous chloride (tin salt) 

Tartaric acid 

Zinc chloride 

Zinc sulphate (white vitriol), crystallized.... 



Soluble in ioo parts by weight of 
water at 



50°F. 


212° F. 


Parts by weight. 


Parts by weight. 


slightly soluble 


slightly soluble. 


very slightly soluble 


decomposable. 


3-2 


28.6 


50 to 66 


very soluble. 


slightly soluble 


slightly soluble. 


37-4 


62 at 158° F. 


soluble 


very soluble. 


c.65 


1.25 


9.8 


357-5 


0.4 


6.9 


109 


156 


94 


154 


soluble 


decomposable. 


8.0 


98 


28 


5° 


soluble 


soluble. 


21. 1 


247 


6.45 


very soluble. 


12.5 


IOO 


58 


very soluble. 


very soluble 


very soluble. 


42 


78.5 


122 at 32 F. 


714 at 185 F. 


227 at 67 F. 


1 1 1 1 at 230 F. 


very soluble 


very soluble. 


12 


45 


40 


540 at 219.2 F. 


36 


40.7 at 21 5. 6° F. 


108.5 


163 


96.x 


213 


65 


102 at 140 F. 


20 


15° 


6.8 


93 


9 


42.5 


2 5 


IOO 


soluble 


soluble. 


271 


decomposable. 


125.7 


343-3 


300 


very soluble. 


138.2 


653.6 



700 APPENDIX. 

Content of Metal in the Most Commonly Used Metallic Salts. 



Metallic Combination. 



Formula. 



Cobalt ammonium sulphate, crystallized... 

Cobalt chloride 

Cobalt sulphate, crystallized 

Copper acetate, crystallized (verdigris) . . • 

Copper carbonate 

Copper chloride, crystallized 

Copper cyanide 

Copper oxide, black 

Copper sulphate (blue vitriol), crystallized. 

Cuprous oxide 

Ferrous sulphate (green vitriol), crystal- 
lized 

Gold chloride (brown), technical 

Gold chloride (orange), technical 

Iron-ammonium sulphate, crystallized 

Lead acetate (sugar of lead), crystallized. 

Lead nitrate, crystallized 

Mercuric chloride 

Mercurous nitrate 

Nickel-ammonium sulphate, crystallized. . . 
Nickel carbonate, basic (separated at 

212° F.) 

Nickel chloride, crystallized 

Nickel chloride, anhydrous 

Nickel hydrate 

Nickel nitrate, crystallized 

Nickel oxide 

Nickel sulphate, crystallized 

Platinic chloride 

Platoso ammonium chloride . . 

Potassium-copper cyanide, crystallized, 

technical 

Potassium mercuric cyanide 

Potassium-silver cyanide, crystallized 

Potassium-zinc cyanide, crystallized 

Silver chloride 

Silver cyanide 

Silver nitrate, crystallized 

Stannous chloride (tin-salt") 

Zinc-ammonium chloride 

Zinc carbonate 

Zinc chloride 

Zinc cyanide 

Zinc sulphate (white vitriol), crystallized . . 



(NH 4 ) 2 Co(S0 4 ) 2 +6H 2 

CoCl.,+ 6H. 2 

CoS0 4 +7H 2 

Cu(C 2 H 3 2 ) 2 +H 2 

2CuCO s (CuOH) 2 

CuCl 2 +2H 2 

Cu 3 (CN) 4 + 5 H 2 

CuO 

CuS0 4 +5H 2 

Cu 2 

FeS0 4 + 7H 2 

AuCL,-)-x ag 

AuCl 3 -|x ag 

(NH 4 )Fe(S0 4 ) 2 +6H 2 

Pb(C 2 H,0 2 ) 2 + 3 H 2 

Pb(N0 3 ) 2 

HgCl 2 

Hg,(N0 3 ) 2 

(NH 4 ) 2 Ni(S0 4 ) 2 +6H 2 

NiCO s 4NiO, 5H 2 

NiCl 2 4-6H,0 

NiCl 2 

fNi(OH) 2 +H.,0 (separated \ 



at 212 F.) 
Ni(NCQ 2 +6H 2 

Ni-A 

NiS0 4 +7'H,0 

PtCl 4 + 5 H 2 

(NH 4 ) 2 PtCl B 

K 4 Cu 2 (CN) 6 

K 2 Hg(CN) 4 

KA g (CN) 2 

K 2 Zn(CN) 4 

AgCl 

AgCN 

AgN0 3 

SnCl 2 +2H ? 

NH 4 ZnCl s +2H 2 

ZnCO a Zn(OH) 2 

ZnCl 2 

Zn(CN) 2 

ZnSQ 4 +7H 2 



t 



SIS. 

o ^ 
U 



14.62 

! 24.68 

20.92 

3I-87 
55-2o 
37-°7 
5 6 -5° 
79-83 
25.40 

88.79 

20.14 
50 to 52 
48 to 49 

14.62 

, 54-57 
62.51 

73-87 
79-36 
14.94 

57-87 
24.63 

45-3° 
63-34 
18.97 
71.00 
22.01 
45-66 
43-91 

28.83 

53-56 
54.20 

26.35 
68.20 

80.57 
64.98 

52.45 
28.98 
29.05 
47.84 
56.59 
22.73 



APPENDIX. 



701 



Table Showing the Electrical Resistance of Pure Copper Wire 
of Various Diameters. 







Number of 






Number of 


No. of wire, 




feet required 


No. of wire, 




feet required 


Birmingham 


Resistance of 


to give 


Birmingham 


Resistance of 


to give 


wire gauge. 


i foot in ohms. 


resistance 


wire gauge. 


1 foot in ohms. 


resistance 




O.OOOO516 


of 1 ohm. 






of 1 ohm. 


OOOO 


19358 


17 


O.OO316 


316.I 


OOO 


O.OOOO589 


16964 


18 


O.OO443 


225-5 


OO 


O.OOO0737 


I3562 


19 


O.OO603 


105-7 


O 


O.OOOO922 


IOS57 


20 


O.O0869 


115. 1 


I 


O.OOOII8 


8452.6 


21 


O.OIO4O 


96.2 


2 


O.OCOI32 


7575-1 


22 


0.01358 


73-6 


3 


O.OOOI59 


6300.1 


23 


O.OI703 


58.7 


4 


O.OCOI88 


53I9-9 


24 


0.02200 


45-5 


5 


0.000220 


4545-9 


25 


O.02661 


37-6 


6 


O.CCO258 


387 -3 


26 


O.O3286 


304 


7 


O.OOO329 


3°43-4 


27 


O.O4159 


24.0 


8 


O.OOO39I 


2 557-i 


28 


O.05432 


18.4. 


9 


O.OOO486 


2057.7 


29 


O.063OO 


15-9 


IO 


O.OOO593 


1686.5 


30 


0-07393 


!3-5 


n 


O.OOO739 


i35 2 -5 


31 


O.IO646 


9-4 


12 


O.OO0896 


1 1 16.0 


32 


O.I3T44 


7.6 


13 


O.OO 1 180 


847-7 


33 


O.16634 


6.0 


14 


O.OOI546 


647.0 


34 


O.21727 


4.6 


*5 


O.OO2053 


487.0 


35 


O.42583 


2.4 


16 


O.OO2520 


396.8 


36 


O.66537 


r -5 



Resistance and Conductivity of Pure Copper at Different 
Temperatures. 



Centigrade 
temperature. 


Resistance. 


Conductivity. 


Centigrade 
temperature. 

i6 c 


Resistance. 


Conductivity. 


o° 


I .OOOOO 


I .OOOOO 


I.06168 


.94190 


I 


I. OO38 1 


.99624 


17 


I.06563 


.93841 


2 


I.O0756 


•99250 


18 


I.06959 


•93494 


3 


1-01135 


.98878 


19 


I.07356 


•93H8 


4 


1-01515 


.98508 


20 


I.07742 


.92814 


5 


1.01896 


. -98139 


21 


1. 08 1 64 


•92452 


6 


1.02280 


.97771 


22 


I-08553 


.92121 


7 


1.02663 


.97406 


23 


I.08954 


.91782 


8 


1.03048 


.97042 


24 


I.O9365 


•91445 


9 


I-03435 


.96679 


25 


I.09763 


.91110 


10 


1.03822 


.96319 


26 


I.IOl6l 


.90776 


11 


1. 04 1 99 


•95970 


27 


I. IO567 


•90443 


12 


1.04599 


•95603 


28 


I.II972 


.90113 


13 


1.04990 


•95247 


29 


I.II882 


•89784 


14 


1.05406 


•94893 


30 


I.I 1 782 


.89457 


15 


I-05774 


•94541 









702 



APPENDIX. 



Table of Hydrometer Degrees according to Baume, at 63.5° F., 
and their Weights by volume. 



Degrees 
Be. 


Weight 

by 
volume. 


Degrees 
Be. 


Weight 

by 
volume. 


Degrees 
Be. 


Weight 

by 
volume. 


Degrees 
Be. 


Weight 

by 
volume. 


o 


1 .0600 


19 


1.1487 


38 


1-3494 


57 


1.6349 


i 


1.0068 


20 


1.1578 


39 


1.3619 


58' 


1-6533 


2 


1.0138 


21 


1. 1670 


40 


1-3746 


59 


1. 6721 


3 


1 .0208 


22 


1. 1763 


4i 


1.3876 


60 


1. 6914 


4 


1.0280 


23 


1.1858 


42 


1 .4009 


61 


1.7m 


5 


l -°3S3 


24 


'•«955 


43 


1.4I43 


62 


I-73I3 


6 


1.0426 


25 


1.2053 


44 


1.4281 


63 


1.7520 


7 


1. 050 1 


26 


1-2153 


45 


1. 442 1 


64 


1-7731 


8 


1.0576 


27 


1.2254 


46 


1.4564 


65 


1.7948 


9 


1.0653 


28 


1-2357 


47 


1.4710 


66 


1.8171 


10 


1.0731 


29 


1.2462 


48 


1.4860 


67 


1.8398 


Ti 


1.0810 


30 


1.2569 


49 


1.5012 


68 


1,8632 


12 


1.0890 


31 


1.2677 


5° 


1.5167 


69 


1.8871 


*3 


1.0972 


32 


1.2788 


5 1 


I-5325 


70 


1.9117 


14 


1-1054 


33 


1. 2901 


52 


I-5487 


7i 


i.937o 


J 5 


1.1138 


34 


1.3015 


53 


1.5652 


72 


1.9629 


16 


1. 1 224 


35 


i-3i3i 


54 


1.5820 






17 


1.1310 


36 


1.3250 


55 


1-5993 






18 


1. 1398 


37 


I-3370 


i 56 


1.6169 







Table of 


Bare 


Copper 


Wire for Low Voltage. 




bo 

3 




>. 






CuO 

3 




>> 




u c 
p.— 


M 


s 


fail 


P. U 




M 


4> 


U rt * 


P.U 


V V 


CO 


0) 


rt (\ 


_£'*" 


2 ° S 


GO 


<U 


rt a 


•S"*r 


2 ° E 


<8 


a 


° M 6 


te 

•S ° 


.2 0^3 


*J 


a 


° br g 


.9 8 


.2 ox 
u H O 


m 


O 


co 


£ 


etf 


pa 


P 


CO 


£ 


P< 


0000 


.460'' 


300 


63 lbs. 


.0487 


4 


. 200" 


100 


13 lbs. 


.2624 


000 


.400" 


245 


5° " 


.0682 


6 


.160" 


80 


8 


.4264 


00 


.360" 


215 


40 " 


.0853 


8 


.130" 


60 


5 " 


.5686 





.320" 


190 


31 " 


.1066 


10 


.IOo" 


40 


3 


1.0662 


I 


.290" 


160 


25 " 


.1218 


12 


.080" 


30 


2 " 


1.706 


2 


.260" 


13s 


20 " 


•1550 


14 


.060" 


22 


1.2 ' 


2.843 


3 


.230" 


"5 


16 " 


.2007 


16 


.050" 


15 


.78 " 


4.264 



INDEX. 



ACCUMULATOR,, chemical processes 
in the, 112-1 16 

common form of, 116 

performance of, 185 
Accumulators, 111-118 

coupling of, 118 

installation and, 184-187 

maintenance of, 116-118 
Acid copper baths, examination of, 594- 
596 

free, in acid copper baths, deter- 
mination of, 594 

potassium carbonate, 684 

pump, 233 

regaining of, from dipping baths, 
227, 228 

residue, 54 

salt, 45, 46 

vapors, absorbing plant for, 227 
Acids, 40, 41, 669-673 

formation of salts from, 44 
Albert, Dr. E. , on metal matrices, 603- 

605 
Alexander's patents, 458, 459 
Alkalies and alkaline earths, 673, 674 

poisoning by, 557 
Alliance magnetic-electrical machine, 7 
Alloys, metallic, for moulds, 636, 637 
Alternating actions, electro-magnetic, 18 

currents, generation of, 98 
Aluminium-bronze baths, 359 

deposition of, 483, 484 
upon, 484-486 
Amalgamating articles to be silvered, 

382, 383 _ 
Amalgamation, 71, 72 
Amalgams of potassium and sodium, 4 
Ammeter, 144-147 
Ammonium, 673, 674 

alum, 686, 687 

chloride, 676 

hydrate, 673, 674 

phosphate, 692 

sulphate, 686 

sulphide, 675 
Ampere, 20 

hour, electro-chemical equivalent 
of, 126 



Ampere turn number, 13 
Ampere's rule, 11 

theory, 10, 11 
Analytical chemical process, 32 
Anions, 47 

Anode, definition of, 47 
Anodes, arrangement of, in the bath, 
158-161 

brass. 355 

choice of. 242, 243 

copper, 336 

elliptic, 268-270 

faulty arrangement of, 281, 282 

for galvanoplastic baths, 586, 587 

gas-carbon, 272 

gold, 421-424 

insoluble, 271, 272 

in silver baths, 372 

lead, 472, 473 

nickel, 268-275 

platinum, 271, 272 

retort-carbon, 271 

zinc, 463-465 
Antimony baths, 478, 479 

deposition of, 478, 479, 515 

potassium tartrate, 693 

properties of, 478 

sulphide, 675 

trichloride, 676 
Antique silvering, 405 
Aqua fords, 670 
Areas silver-plating, 380, 381 
Argentiferous paste. 504, 505 
Armature, 95, 97-100 
Arrhenius, investigation of, 51, 52 
Arsenic, 672 

baths, 479-483 

deposition of, 479-482, 515 

properties of, 479 

sulphide, 675, 676 
Arsenious acid, 672 

chloride, 677 

sulphide, 675, 676 
Astatic galvanometer, 12 
Atomic weights, 34, 35 
Atoms, 33, 34 
Avogrado's law, 51 
Avoirdupois weight, 695 



(703) 



704 



INDEX. 



Auric chloride, 679 
Autotypes, batli for, 590 

BABY shoes, coppering, 656 
Bacco's coppering bath, 495, 496 
Backing deposit or shell, 617, 618 

metal, 618 
Baking powder, 684, 685 
Balance, voltametric, 391-394 
Balances, metalloinetric, 388-391 
Barium cyanide, calculation of quantitv 

of, 410, 411 
Bases, 41 

Basse and Selve's patent, 492, 493 
Bath, arrangement of objects and anodes 
in, 158-161 
determination of current-output of 

a, 127, 128 
electro-cleaning, arrangement of a, 

230, 231 
genera] qualifications of a, 246 
Baths, 233-246 

agitation of, 236-240 
boiling of, 240, 241 
concentration of, 235, 236 
current-densities and electro-motive 

forces required for, 168, 169 
distinction between, 245 
dynamo for series coupling of, 171 
effect of current-density on, 244, 245 
filtering of, 242 
galvanoplastic, agitation of, 581 -586 

coupling, 570-573 
glycerin in place of water for pre- 
paring, 251, 252 
prevention of impurities in, 242 
reaction of, 245, 246 
temperature of, 236, 240 
working of, with the current, 241, 
242 
Batteries, plunge, 84-87 
Battery, galvanic or voltaic, 31 

galvanoplastic deposition with, 567, 
568 
Baume hydrometer degrees and their 

weights by volume, 702 
Belt-attachment combined with double 
grinding lathe, 202 
strapping attachment, 212 
Bertrand's palladium bath, 449 
Bicarbonate of potash , 684 
Bichromate cell, 87 

Bicycle frames, removing hard solder 
from, 221, 222 
parts, nickeling of, 277 
Bird, production of amalgams of potas- 
sium and sodium by, 4 
Bivalent and trivalent elements, 38 



Bivalent elements, 38 
Black lacquers, spraying, 551-553 
leading machines, 610-613 
nickeling, 260-262 
sulphide of antimony, 675 
Blassett, E. , Jr. , arsenic baths given by, 

481,482 
Blue copperas, 687, 688 
vitriol, 687, 688 

solution, electrolysis of, 56 
Bobs, cloth, 207 

construction of, 299 
Boiling baths, 240, 241 
Boettger's discoveries, 6, 7 

iron bath. 476 
Boric acid, 671, 672 

addition of, to nickel baths, 
250, 251 
Boudreaux brushes, 102 
Bower-Barff. dead black lacquer as sub- 
stitute for, 547, 548 
Bowls, galvanoplastic decorations on, 

651-656 
Branch conductors, 153 

wires, 26 
Brandley's method of making gelatine 

moulds, 645 
Brass anodes. 355 
baths, 349-354 

examination of, 360-362 
tanks for, 355 
bedsteads, lacquering, 545, 546 
black on, 526, 527 
brown on, 528. 529 
castings, grinding of, 206 
color resembling gold on, 527, 528 
coloring of, 525-531 
cornflower-blue on, 529, 530 
dead red on, 529 
deposition of, 348-362 
deposits, polishing of, 216 
Ebermayer's experiments in color- 
ing, 530, 531 
etching, 630 
gold color on, 527 
nieling upon, 404, 405 
patina for, 524 
objects, cleaning of, 232, 233 

pickling of, 223, 224 
salts, prepared, 354, 355 
scratch-brushes for, 214 
sheet, brushing of. 206 

nickeling, 306 
silver color on 527 
steel-gray on, 527 
straw-color, to brown, through 
golden yellow, and tombac color 
on, 527 



INDEX. 



705 



Brass, tin bath for, 451, 452 
tinning solution for, 513 
varieties of, 348 
various colors on, 525 
violet on, 529, 530 
zincking, 514 
Brassed castings, prevention of stains 

on, 337 
Brassing by contact, 498, 499 

execution of, 355-360 
Bright dipping bath, 223 

plating, preparations for, 377-379 
Platinum Plating Co. , platinum 
bath of, 445 
Britannia, cleaning of, 233 

direct silvering of, 401, 402 
Bronze Barbedienne, 528, 529 
baths, 363, 364 

clay yellow to dark brown on, 529 
dead yellow on, 529 
deposition on, 363, 364 
objects, cleaning of, 232, 233 
pickling of, 223. 224 
Browning gun barrels, 533 
Brugnatelli. first practical results in 

electro-gilding attained by, 3 
Brush brass dip lacquer and brush brass 
thinner, 545 
finish lacquers. 544 
-coppering, 497, 498 
-holders, 102 
-rocker, 102 
Brushes, 100, 101, 192 
Buck, J., patent of, 384 
Buffing lathes, electrically driven, 211 
Bunsen cell, 75-81 

process which takes place in 

the, 76 
treatment of, 80. 81 
Burgess, experiments by, regarding 
zincking by the hot process and 
electro-deposition, 455-458 
on removing hard solder from bi- 
cycle frames, 221, 222 
and Hambuechen, process of plat- 
ing aluminium by, 485, 486 
Burnishing, 213, 216, 217 
Burnt nickeling, 278, 279 
Busts, coppering, 650 

galvanic reproduction of, 634-645 
Butter of antimony, 676 
of zinc, 677 

pADMIUM silver bath, 380, 381 
\J Calcium carbonate, 685 

hydrate, 674 
Candelabras, coppering, 656, 657 

45 



Cane handles, celluloid, galvanoplastic 

decorations on, 656 
Carbon, artificial, preparation of, 75 
blocks, coppering, 656 
disulphide, 675 

addition of, to nickel baths, 263 
of, to silver baths, 377-379 
pins, coppering, 656 
Carbonates, 684-686 
Cast iron, pickling of, 218-220 
rolls, coppering, 656 
tanks, enameled, 154 
tin bath for. 451, 452 
Castings, pickled, dip lacquer for, 542, 

543 
Cathode, definition of, 47 

separation of metal on, 56, 57 
Cations, 47 
Caustic potash, 673 
soda. 673 

electrolysis of, 55, 56 
Cell apparatus, copper bath for, 564, 565 
galvanoplastic deposition in, 
561-566 
galvanic or voltaic, 31 
Cells, coupling, 87-90, 132-135 

for galvanoplastic deposition by 

battery, 567 
forms of, 561-563 
installations with, 132-164 
secondary, 111-118 
voltaic, 70-84 
Celluloid umbrella and cane handles, 

galvanoplastic decorations on, 656 
Centigrade degrees of thermometer, 
conversion of to Fahrenheit degrees, 
696 
Centrifugal dryer, 164 
Chalk, 685 

Chemical compounds, table of solubili- 
ties of, 698, 699 
elements, 33 

energy of, 53, 54 

symbols of, 34 

table of the atomic weights of 

the most important, 35 
valence of, 36-38 
formulas, 35, 36 
principles, fundamental, 31-46 
processes, 32 

in the accumulator, 112-116 
treatment of objects, 218-233 
Chemicals, poisoning by, 556, 557 
purity of, 234, 235 
used in electroplating and galvano- 
plasty, 669-694 
Chile saltpetre, 690 
China, silver deposit on, 652-656 



706 



INDEX. 



Chloride of zinc and ammonia, 678 
Chlorine combinations. 676-680 

-ions, properties of, 48 

poisoning by, 557 
Christofle & Co., early use of magnetic- 
electrical machines by, 7 
Chrome gelatine, 626,627 
Chromic acid. 672 
Circuit, closed, 80 
Citric acid, 671 

Clamond's thermo-electric pile, 91, 92 
Classen's patent, 461 
Clausius, theory of, 50 
Clay objects, coppering, 650 
Cleaning and rinsing apparatus, 161- 
164 

electro-chemical, 229-231 

polished objects. 217. 218 
Cliches, nickeling. 312-314 
Clock cases, mat black coaling on, 535 

gilding, bath for, 418, 419 
Closed circuit. 30 
Cloth bobs, 207 
Cobalt-ammonium sulphate, 689 

baths, 323, 324 

deposition of, 323-325 

properties of, 323 
Cobalting by contact and boiling, 494, 

495 
Cobaltons carbonate, 686 

chloride. 678 

sulphate. 689 
Coefficient of temperature, 26 
Coehn and Siemens, investigations by, 

268 
Coffee sets, galvanoplastic decorations 

on, 651 
Colcothar, 212 

Cold silvering with paste, 504, 505 
Coloring metals. 516-537 
Commutator, 100. 101 
Compound-wound dynamos, 105 
Concentration of baths, 235, 236 
Conducting fixtures, 157, 158 

salts, 249, 250 
Conductors, 29, 46. 152-154 
Connection of main and branch con- 
ductors, 154 
Conservation of force and work, 53 

matter, law of, 33, 53 
Contact, deposition by, 487-491 

-electricity, 29-31 
discovery of, 1, 2 

metals, 489 
Contacts, 153 
Copper acetate, 693, 694 

alloys, nickel bath for, 258, 259, 
260, 262 



Copper anodes, 336 

bath for incrusting galvanoplasty, 

649 
baths, 326-333 

acid, examination of, 594-596 
containing potassium cyanide, 

examination of. 342-318 
determination of copper in, 
345-348 
of potassium cyanide in, 
343-345 
galvanoplastic, 564, 565, 574, 
" 575, 586 

without potassium cyanide. 
334. 335 
black on, 521, 522 
blue-black on. 520 
brass and bronze, deposition of, 

326-364 
bronzing of. 519 
brown on, 518, 519 

layer of cuprous oxide on, 518 
of various shades on, 518, 519 
carbonate, 685 
castings, grinding of, 206 
chloride, 677 
cleaning of. 232, 233 
coloring. 517-525 
cyanide, 682 

baths. 327-334 

preparation of, 327 
tanks for, 385, 3 6 
thickening of, 341 
dark brown to black on, 520 
deposited, properties of, 575 
deposition of, 326-3 18 
deposits, brittle. 578. 579 

from metallic surfaces, 620-622 
polishing of, 216 
determination of, in brass baths, 
360. 361 
of, in copper baths. 345-3*8 
galvanoplasty in. 559-657 
gold yellow on, 519 
in acid copper baths, determination 

of, 594, 595 
nickel bath for, 258, 259, 260 
patina for. 524 
pickling of, 223, 224 
plates, etching. 630 
properties of, 326 
pure, resistance and conductivity 

of, 701 
quantity of, liberated from cupric 

salts, 60 
red to violet shades on, 521 
salts, poisoning by, 556, 567 
scratch-brushes for, 21 4 



INDEX. 



707 



Copper sheet, brushing of, 206 
nickeling, 306 
steel-gray on, 524, 525 
sulphate, 687, 688 
tin bath for, 451, 452 
tinning solution for, 513 
tubes, production of, 646 
various colors on, 525 
wire, bare, for low voltage, table 
of, 702 
pure, table of electrical resist- 
ance of, 701 
silvering, 403 
yellowish brown on. 519 
zinc alloy, solution for transferring 

any, 354 
zincking, 514 
Copperas, 687, 688 

Coppered art castings, inlaying of de- 
pressions of, 341, 342 
castings, prevention of stains on, 

337 
objects, coating of, with another 
metal, 340 
Coppering by contact and dipping, 495- 
498 
execution of, 336-342 
Knight's process of, 591 
salts, prepared, 333, 334 
small articles in quantities, 341 
stereotypes, 622, 623 
zinc plates, 623 
Corvin's niello, 646, 647 
Coulomb, 20 
Counter-current, appearance of, 66, 67 

-force, 53 
Coupling accumulators, 118 
cells, 87-90, 132-135 
main object wire and main anode 
wire, together with the resistance 
boards, voltmeter, switch and 
two baths, 148-151 
Covering ground, 624 
Cream of tartar, 692, 693 
Cruikshank, investigations by, 3 

trough battery devised by, 2, 71 
Cubic nitre, 690 
Cuivre fume, 520, 521 
Cupric oxide cell, 82, 83 

salts, quantity of copper, liberated 

from, 60 
sulphate, 6S7, 688 

solution, electrolysis of, 56 
Cupro-cupric sulphite, 332 
Cupron cell, 83, 84 
Cuprous cyanide, 336 

oxide, regeneration of, 83 
sulphite, 690 



Cups, gilding inner surfaces of, 428 
Current, branching or distributing the, 
26_ 
conditions for galvanoplastic baths, 

576-578 
coupling cells for quantity of, 89 
-density, 124-130 

calculation of quantity by 
weight of deposit from, 125, 
126 
dependence of, on electro- 
motive force. 151, 152 
effect of in baths. 244, 245 

nickel baths, 252 
for nickeling, 279-281 
-distribution, two and three-wire 

systems of, 179. 180 
electro-motive force of, 20, 21 
in a Daniell cell, 64, 65 
-indicator, 139-141 
-lines, scattering of. 132, 275 
osmotic theory of the production 

of, 63-65 
-output, 245 

of a bath, determination of, 
127, 128 
preparation of gold baths with the 

assistance of, 420, 4ll 
primary, inducing or main, 16 
-regulation, 135-139 
secondary, induced, or induction, 

16 
sources of, 70-118 
-strength, calculation of, 126, 127 
calculation of weight of silver 

deposit from, 398-400 
unit of, 20 
working baths with, 241. 242 
Currents, alternating, generation of, 98 
Cyanide combinations, poisoning by, 556 
Cyanides, 680-684 

metallic, first use of solutions of, 
in potassium cyanide, 6 

DANEEL on changes in concentration 
of baths, 238, 239 
Daniell cell, 73, 74 

current in a, 64, 65 
process which takes place in 
the, 73, 74 
Darlay's patented baths, 493, 494, 496, 

497, 498, 499,500,512,514 
Davy, Sir Humphry, discovery of the 

metals sodium and potassium by, 3 
Dead black lacquers, 546-548 
Decomposition-pressure, 67, 68 
Deposit, absorption of, 243 
backing, 617, 618 



708 



INDEX. 



Deposit, detaching the, from the mould 
615-617 
formation of. 213, 214 
Deposition by contact, 487-491 

by boiling, and by 
friction, 487 
galvanoplastic, duration of, 579, 580 
of aluminium, 483, 484 
antimony, 478, 479 
arsenic, 479-482 
brass, 348-362 
bronze. 363, 364 
cobalt, 323-325 
copper. 326-348 
iron, 475-477 
lead, 472-175 
nickel, 247-323 
palladium, 448, 449 
platinum, 444-448 
silver, 365-414 
tin, 450-453 
tombac, 362, 363 
zinc, 453-472 
upon aluminium, 484-486 
Deposits, high luster on, 216, 217 
scratch-brushing of, 213-215 
De Ruolz. first deposition of metallic 

alloys by, 7 
Dieffenbach and Limpricht's patent, 

646 
Difference of potential, 21 
Dip lacquer for pickled castings to be 

copper-plated or oxidized, 542, 543 
Dipping and pickling, 218-228 
baskets, 294 

baths, regaining acid from, 227, 
228 
Direct acting dynamos, 103-108 
Dissociation, electrolytic. 50-52 
Donath's patinizing fluids, 523 
Drum armature, 97, 98, 99 
Drying, 215, 216 

barrel, steam, 164 
Du Fresne's process of gilding, 433 
Dust, devices for keeping the, out of 

polishing room, 123 
Dynamo and accumulators, combined 
operation with, in galvanoplasty, 
573 
choice of a, 167-172 
electric machines, 93-111 

fundamental principles 

of, 94, 95 
impetus given by, to the 
electro-plating indus- 
try, 8 
installations with, 164- 
183 



Dynamo electric machines, separate 
parts of, 96-103 

galvanoplastic deposition with, 568— 
573 

impressed electro-motive force of, 
168, 169 

setting up and running a, 164-167 
Dynamos, direct acting, 103-108 

parallel coupling and series coup- 
ling of, 172-175 

EBERMAYER'S experiments in col- 
oring brass, 530, 531 
silver immersion bath, 503 
Eichstaedt, T. C, on keeping dust out 

of polishing room*, 123 
Egyptian Lacquer Manufacturing Co.,. 
bcquers made by, 542, 543, 545, 548, 
554 
Elb's theory of the chemical processes 

in the accumulator, 112-115 
Electric current, comparison of, with a 
current of water, 19, 20 
induction, discovery of, 4 
resistance of pure copper wire, table 
of, 701 
unit of, 22 
units, 18 24 
work, unit of, 21 
Electricity, contact, 29-31 

discovery of, 1, 2 
frictional. 28, 29 
kinds of. 29 

unit of the quantitv of, 20 
Electro-chemical cleaning, 229-231 
equivalent, 60. 61 
means, matting by, 434, 435 
-chemistry, fundamental principles^ 

of, 46-69 
-deposition, production of colors on 

metals by. 536, 537 
-engraving. 631-634 
-etching. 623-625 
-magnetic alternating actions, 18 

induction machine, first, 4 
-magnetism, 11-15 
-magnets, 12 

-metallurgy, first application of the 
term, 6 
historical review of, 1-8 
-motive counter-force of polariza- 
tion, 130 132 
force, coupling cells for. 89 
dependence of current-den- 
sity on, 151. 152 
difference of, 21 
for nickel baths, 252 
in cell-apparatus, 566 



INDEX. 



709 



Electro-motive force of current, 20, 21 
series of, HO 
unit of, 21 
-plating apparatus, mechanical, 
295-298 
arrangements in particular. 

124-132 
chemicals used in, 669-694 
mechanical treatment during 
and after, 213-218 
treatment previous to, 
188-213 
plant, actual parts of a, 124 
arrangement of, in general, 

119-187 
with dynamos, ground plans 
of, 175-180 
process, wrong ideas of, 188, 

189 
solutions, 233-246 
-silvering, special applications of, 

403-405 
-technics, fundamental principles 
of, 18-28 
table of solubilities of chemical 
compounds, used in, 698, 699 
Electrochroma, 536, 537 
Electrochroiny, 473-475 
Electrodes, definition of, 47 
processes on the, 54-58 
Electrolysis, definition of, 47 

determination of copper in copper 
baths by, 345. 346 
of zinc in brass baths by, 361 
Electrolyte, electrolysis of a, between 
insoluble electrodes, 66 
resistance of, 128-130 
Electrolytes, 46, 47, 2H3-246 
Electrolytic analysis, 319-323 
dissociation, 50-52 
pickling, 220, 221 
Electrotvpes, duration of deposition for, 
580 
finishing, 618-620 
iron, 657-661 
nickel, 661-664 
Electrotypy, 561-634 
Elements, chemical, 33 

energy of, 53, 54 
symbols of, 34, 36 
table of the atomic 

weights of the, 35 
valence of, 36-38 
Elmore's process of producing copper 

tubes, 646 
Eisner's bronze bath, 363 

tinning bath, 513 
Emery, kinds of, 198 



Enclosure work, interior, lacquer for, 

541, 542 
Endless belt machine, 212 
Energy, 52-54 
Etching ground, 624 

FAHRENHEIT degrees of thermom- 
eter, conversion of, to Centigrade 

degrees, 696 
Faraday, electric induction discovered 

. by, 4 

investigations of, 59 

laws of, 58-60 
Feelers, 613 

Fein's plunge battery, 85 
Ferric oxide, 212 

sulphide, 676 
Ferrous sulphate, 687 
Field, magnetic, 11, 13 

magnets, 96 

winding, 96 
Filtering baths, 242 
Fire gilding, combination of, with 

electro-deposition, 433 
Fischer's method of making impres- 
sions, 609 
Fleming's hand rule, 18 
Floors of plating rooms, 121, 122 
Flowers, coppering. 650 
Fluid, evaporation of a, 61 

measure, imperial, 696 
Foerster, experiments of, 267 

and Seidel on mechanical proper- 
ties of deposited copper, 575 
Force, 53 

and work, conservation of, 53 
Foreign excitation, 97 
Forks, calculation of time for deposi- 
tion of determined weight on, 127 

extra heavy coating of silver on, 
383, 384 
Four-polar dynamo, 96 
French form of cell apparatus, 562, 563 
Frictional electricity. 28, 29 
Frosting silver, 400, 401 

GAIFFE'S cobalt solution, 323, 324 
Galvani, discovery of contact-elec- 
tricity by, 1, 2 
Galvanic cell 31 
current, 31 

reproduction of plastic objects, 634- 
645 
Galvanometer, indications made by, 

142-144 
Galvanometers, 12, 139, 140 
Galvanoplastic baths, agitation of, 
581-586 



710 



INDEX. 



Gal vano plastic baths, current conditions 
for, 578 
deposition by battery and dynamo, 
566-573 
duration of, 579, 580 
in the cell-apparatus, 561-566 
method for originals in high relief. 

643, 644 
process, discovery of, 5 
reproduction for graphic purposes, 
561-634 
Galvanoplasty, 558-668 

chemicals used in, 669-694 

for graphic purposes, operations in, 

596-645 
in copper, 559-657 
iron (steel), 657-661 
nickel, 661-667 
silver and gold, 667, 668 
incrusting, 647-649 
rapid, baths for, 590, 592 
special applications of, 645-657 
Galvanoscopes, 12 
Gas-carbon anodes, 272 
Gases, solutions of, 48 
Gassiot's process for obtaining metallo- 

chromes, 474, 475 
Gauduin's copper bath, 335 
Gauze, gilding of, 437-440 
Gelatine moulds, 644, 645 
German form of cell apparatus, 563 
silver, direct silvering of, 401. 402 
objects, cleaning of, 232, 233 

pickling of, 223, 224 
sheets, brushing of, 206 
Gilded articles, stripping gold from, 

440, 441 
Gilder's wax, 436 

Gilding by contact, by immersion, and 
by friction, 508-511 
coloring of, 435-437 
combination of fire-gilding with 

electro-deposition, 433 
genuine, determination of, 441 
green, 431,432 
improving bad tones of, 437 
inner surfaces of hollow-ware, 428 
mat, 434, 435 

metallic wire and gauze, 437-440 
red. 430, 431 

reddish, by friction, 510. 511 
rose color, 432 
without a battery. 426 
Girders, wrought iron, zincking of, 468, 

469 
Glass, galvanoplastic decorations on, 
651-656 
silver deposit on, 652-656 



Glauber's salt, 686 

Glycerin, preparation of baths with, 233 
substitution of, for water, 251, 252 
Gold and silver, galvanoplasty in, 667, 
668 
anodes, 421-424 
baths, 416-421 

examination of, 441 , 442 
heating, 425 
management of, 421-424 
recovery of gold from, 442, 443 
tanks for, 424-426 
chloride, 679 
deposition of, 415-443 
deposits, burnishing of, 216, 217 

polishing, 429 
estimating the fineness of, 415, 416 
incrustations with, 403, 404 
old, 432, 433 

plating, execution of, 426-430 
properties of, 415, 416 
recovery of, from gold baths, 442, 

443 
stripping from gilded articles, 440, 
441 
Goldberg's patent, 461 
Gore's antimony bath, 479, 480 
brass bath, 353, 354 
process for silvering, 402 
Gottig's process of plating aluminium, 

486 
Gountier's bronze bath, 363 
Graining, 505-508 
Gramme-equivalent, 60 
Gramme's machine, introduction of, 8 
Graphic purposes, galvanoplastic repro- 
duction for, 561-634 
operations in galvanoplasty 
for, 596-645 
Grasses, coppering, 650 
Gray, discoveries of, 29 
Grease, removal of, 228, 229 
Green gilding, 431, 432 

vitriol, 687 
Grille work, interior, lacquer for, 541, 

542 
Grinding, 196-199 

and brushing, execution of, 204-206 

polishing rooms, 122, 123 
lathes, 200-204 

motors, electrically driven, 202-204 
wheels, 196-199 

removing emerv and glue from, 

199, 200 
treatment of, 199, 200 
Group coupling, 89 
Giilcher's thermo-electric pile, 92, 93 
Gun barrels, browning, 533 



INDEX. 



711 



Gutta-percha, introduction of, 6 
lacquer, 640 
moulding in, 597 

with, 636 
moulds, detaching deposit 
from, 615, 616 
electrical contact of, 613 

HABEK'S proposition. 257 
Haen's method of determination 
of content of copper in acid 
copper bath. 594, 695 
Haloid acids, 41 
Hand rule, Fleming's, 18 
Hansjosten, J. H. , on pickling cast iron, 

218-2.0 
Hanson & Van Winkle Co.'s acid pump, 
233 
belt strapping attach- 
ment, 212 
centrifugal dryer. 164 
electrically driven 
grinding motors, 
202-204 
elliptic anodes, 268- 

270 
independent spindle 
polishing and buff- 
ing lathe, 210. 211 
mechanical electro- 
plating apparatus, 
296, 297 
motor-generator sets, 

109,110 
multipolar dynamo, 

10., 107 
patent underwriter's 

rheostat, 140, 141 
plating room, 179.180 
separately excited 

dynamo, 108 
special rheostat, 141 
union canvas wheel, 

207 
universal polishing 

wheel. 207 
walrine wheel. 208 
Waverlv voltmeter, 
146, i47 
Hard nickeling, 312 
Haswell's patina, 533 
Heating plating rooms, 120, 121 
Hefner-Alteneck's machine, introduc- 
tion of, 8 
Heliography, 630, 631 
Helios dip lacquer, 543 
Helmholtz, law of Faraday expressed 
by, 60 



Hess' solution for transferring any 
copper-zinc alloy, 354 

Hildi- brand, O. , on regenerative pro- 
cess of electro-zincking, 459. 460 

Hollow-ware, gilding inner surfaces of, 
428 

Holmes magnetic-electrical machine, 7 

Hooks and eyes, silvering. 503, 504 

Hossauer's copper bath, 328 

Hiibl, experiments by, 559, 560 

Hummel's patent, 145 

Hydraulic press, 601, 602 

Hydrochlorate of zinc, 677 

Hydrochloric acid, 670 

dilute, electrolysis of, 55 
removal of, from the 
pores of coppered ob- 
jects, 339 

Hydrocyanate of silver, 683 
zinc. 683 

Hydrocyanic acid, 670, 671 

Hydro-electric current, 31 

Hydrofluoric acid, 672. 673 

Hydrometer degrees according to Baume 
and their weights by volume, 702 

Hydroxyl groups, 41 

Hydroplatinic chloride, 679, 680 

Hydrosulphate of ammonia, 675 

Hydrosulphuric acid, 674 

Hygienic rules for the workshop, 555- 
557 

Hyponitric gases, poisoning by, 557 

TDIO-ELECTRfCS, 28 
J- Imperial fluid measure, 696 
Impurities in baths, prevention of, 242 
Incrusting galvanoplasty, 647-649 
Incrustations with silver, gold and other 

metals, 403, 404 
Induced current, 16 
Inducing current, 16 
Induction, 15-18 

-current, 16 

elect ric, discovery of, 4 

magnetic, magnitude of, 15 
Inductor, 97-100 
Insulating joints, 157 
Ions, 47, 48 

power of entering into chemical 
processes possessed by, 54 

velocity of, 68. 69 
Iridescent colors, 473-475 
Iron-ammonium sulphate, 687 

baths, 475, 476 

management of, 476, 477 

black on. 533-535 

blue on, 535 

brassing bath for, 352, 353, 354 



712 



INDEX. 



Iron, bronze bath for, 363 

brown-black coating with bronze 

luster on, 5b5 
cast, tin bath for, 451, 452 
castings, unground, brassing of, 360 
cleaning of, 232 
coloring, 533-535 
copper baths for, 329, 330 
deposition of, 475-477 
direct silver-plating of, 402 
electrotypes, 657-661 
galvanoplasty in. 657-661 
girders, zincking of, 468, 469 
grinding of, 205 
nickel bath for, 262 
nickeled, prevention of rusting of, 

277, 278 
patina for, 533 
pickling of, 218-220 
sheet, nickeling, 306, 307 

zincking, 466, 467 
silvering of, 500 
silvery appearance with high luster, 

to give, 535 
tinning solution for, 512, 513 

JACOBI, Prof., discovery of the gal- 
vanoplastic process by, 5 
Jordan. C. J., claim by, 5 
Jordis's platinum bath, 445, 446 

standard formula for copper bath, 
328 
Joule, law of, 28 

KA YSER'S process of coloring brass, 
527, 528 
Kirchhoff, law of, 26, 27 
Klein, production of iron electrotypes 

by. 657 
Knife blades, nickeling, 310, 311 
Knight's process of coppering. 591 
Knives, calculation of lime for deposi- 
tion of determined weight on, 127 
nickel bath for, 263 
silver-plating steel blades of, 385, 
386 
Kohlrausch, F. and W., determinations 

by, 60 
Kruel's brass bath, 349 
Kugel. Dr.. discovery by, 266 
Kunze's patent, 609 

LACES, coppering, 649, 650 
Lacquer, application of, 538 
special invisible, for ornamental 
cast and chased interior grille, 
rail and enclosed work, 541, 
542 



Lacquering, 538-554 
Lacquers, dead black, 546-548 
improvements in, 539 
pyroxyline, 539-541 
requisites of, 539 
spraying, 548-553 
water-dip, 553, 554 
Lamp-feet, nickeling of, 283 
Langbein & Co. 's belt-attachment com- 
bined with double grind- 
ing lathe, 202 
two-polar and four-polar 

dynamos, 96 
two-pole shun t-w ound 

dynamo, 104, 105 
voltametric controlling ap- 
paratus, 396-398 
Lathes, grinding, 200-204 

polishing 208-212 
Law of Avogadro, 51 

conservation of matter, 33, 53 
Joule, 28 
Kirchhoff - , 26, 27 
Ohm, 22-24 

proposition deduced from, 90 
Laws of Faraday. 58, 60 
Lead acetate, 694 

and tin, soft alloys of, nickeling, 

311 
anodes, 472, 473 
baths, 472, 473 
cleaning of, 233 
deposition of, 472-475 
salts, poisoning by, 557 
Leather, plates for the production of 

imitation of, 647 
Leaves, coppering, 650 
Le Blanc, decomposition values found 

by, 68 
Leclanche" cell, 81, 82 
Le Fort. A. A., process for silver de- 
posit on glass and china by, 652-656 
Lenoir's process of moulding, 643, 644 
Liebenow's theory of the chemical pro- 
cesses in the accumulator, 115, 116 
Light in plating room, 119 
Lime, burnt or quick, 674 
Line, neutral, 10 
Litmus paper, 42 
Liver of sulphur, 674, 675 
Loadstone, 9 

Liidersdorff's bath for coppering, 495 
Lunar caustic, 691, 692 

MACHINES, distance between, 124 
Magnesian stone, 9 
Magnet, artificial, 9 
winding, 96 



INDEX. 



713 



Magnetic field, 11, 13 

induction, magnitude of, 15 

iron ore, 9 

lines of force, flow of, 13 

machine, first, for the deposition of 

silver, 7 
meridian, 10 
needle, deflection of, 3, 4 
poles, 10 
Magnetism, 9-11 

and electricity, 9-69 
remanent or residual, 13 
Magnitude of the magnetic induction, 15 
Main conductors, 153 
current, 16 
wire, 26 
Manduit's process of bronzing copper, 

519 
Mannesmann Pipe Works process of 

plating aluminium, 486 
Marble, 685 

Marino's patent, 233, 251 
Mat dip, 225 

dipping, 224-226 
gilding, 434, 435 

grained surface, production of, 225 
silver, 400 
Matrices in plastic material, preparation 
of, 596-600 
nickel, 664-667 
Measure, imperial fluid. 696 
Measuring instruments, 144-147 
Mechanical electro-plating apparatus, 
295-298 
treatment during and after electro- 
plating, 213-218 
previous to electro-plating, 
188-213 
work, effect of, 52 
Meidinger cell, 74, 75 
Mercuric nitrate, 691 
Mercurous nitrate, 690, 691 
Mercury salts, poisoning by, 557 
Meridian, magnetic, 10 
Meriten's process for black on iron, 

534, 535 
Metal, content of, in metallic salts, 700 
matrices, 602-609 

detaching moulds from, 617 
Metallic alloys, first deposition of, 7 
moulds, 636, 637 
objects, preparation of, 188-246 
paint, preparation of, 652, 653 
salts, content of metal in, 700 

decomposition-value of solu- 
tions of. 68 
Metallization by dry way, 640. 641 
wet way, 641-643 



Metallized silver, preparation of, 652 
Metallizing moulds. 640-643 
Metal lo-chromes, 473-475 
Metalloids, classification of, 40 
Metallometric balances, 388-391 
Metals and non-metals, 38-40 

classification of, 40 

coloring of. 516—537 

incrustations with, 403, 404 

series of electro-motive force of, 30 

solution-tension of, 61-63 

specific resistance of, 25, 26 
Mirrors, coppering, 651 
Mixed coupling. 89 
Molecular weights of dissolved bodies, 

method of determining, 50, 51 
Molecule, 33 

Molecules, dissociation of, 50 
Monopotassic carbonate, 684 
Montgomery, Dr., introduction of gutta- 
percha by, 6 
Motor-generators, 109, 110 
Mould, detaching deposit from, 615-617 

holder, 614 

suspension of, in the bath, 615 
Moulds, electrical contact of, 613-615 

further manipulations of, 610 

gelatine, 644, 645 

in plastic material, preparation of, 
596-600 

making the, conductive, 610-613 

metallic. 636, 637 

metallizing or rendering conduct- 
ive, 640-643 

non-metallic, rendering of, imper- 
vious. 640 

plaster of Paris for casts, 637-639 
Miiller and Behntje, investigations by, 

579 
Multipliers. 11, 12 
Muriate of gold, 679 
zinc, 677 
Muriatic acid, 670 
Murray, discovery by, 5 
Mylius and Fromm, researches by, 560 

NAILS, zincking, 471 
Nature printing, 645, 646 
Needles' eyes, coppering, 498 
Negative electricity, 29, 47 
Nernst's osmotic theory of production 
of current, 63-65 
theory, 31 
Neubeck's iron electrotypes, 660 
tin bath, 453 

voltametric controlling apparatus, 
394-396 
Neutral line or zone, 10 



714 



INDEX. 



Neutral salts, 44, 46 

Neutralization, 42 

Nicholson and Carlisle, decomposition 

of water by. 3 
Nickel alloys, deposition of. 314, 315 
-ammonium sulpbate, 688, 689 
and cobalt, deposition of, 247-325 
anodes, 268-275 

reddish tinge on, 274, 275 
solution of, 275 
bath, black, 260, 261, 262 

coupling cells for, 133, 134 
current-strength required for, 

125 
without nickel salt, 264 
baths, additions to. 250-252 
carbon disulphide in, 263 
cold, thick deposits in, 267, 

268 
correction of reaction of, 265 
effect of current-density in, 252 
electro-motive force for, 252 
examination of, 316-323 
faulty arrangement of anodes 

in, 281. 282 
formulas for, 253-264 
hot, thick deposits in, 265-267 
insoluble anodes for, 271, 272 
mixed anodes for, 257, 258 
polarization phenomena in, 

284, 285 
proportion of cast to rolled 

anodes in. 273, 274 
reaction of, 252, 253 
recovery of nickel from old, 314 
refreshing, 290, 291 
suspension of objects in, 278 
working of, 264 
-bronze, 315 
carbonate, 685, 686 
chloride. 678 

copper-zinc alloy, deposition of, 315 
deposition of, 247-323 
deposits, polishing of, 216 

thick, in cold nickel baths, 
267, 268 
in hot nickel baths, 265- 
267 
very thick, 262, 263 
electrotypes, 661-664 
galvanoplasty in, 661-667 
matrices, 664-667 
objects, polished, cleaning of, 291, 

292 
properties of, 247, 248 
recovery of. 314 
salts, 248, 249 

prepared, 264. 265 



Nickel, scratch brushes for, 214 

solutions, eruptions caused by, 556 

sulphate, 688 

various colors on, 525 
Nickeled objects, freeing of, from moist- 
ure, 216 
Nickeling by contact and boiling, 491- 
494 

black, 260-262 

burnt, 278, 279 

cavities and profiled objects, 282- 
284 

current density for, 279-281 

dark, 259, 260 

defective, rdsume of, 288-290 
stripping, 285-288 

execution of, 275-285 

hard, 312 

knife blades, 310, 311 

operation, calculation of, 292, 293 

printing plates, 312-314 

quick, 266 

security against rust in, 276-278 

sharp surgical instruments, 310, 311 

sheet-zinc, 298-306 

small and cheap objects, 293-298 

soft alloys of lead and tin, 311 

tin-plate, 306 

treatment of articles after, 291 

wire, 307-309 

yellowish tone of, remedy against, 
288 
Niel, imitation of, 404. 405 
Niello, Corvin's, 646, 647 
Nitrate baths, 580, 581 

of mercury, 691 
Nitrates, 46, 690-692 
Nitre. 690 
Nitric acid, 670 

Nitrous gases, poisoning by, 557 
Nobili, production of iridescent colors 

by, 4 
Nobili' s rings, 473-475 
Noe's thermo-electric pile, 91 
Non-electrics, 29 
Normal salts, 46 
North pole, 10 

Numerical data, useful, table of, 696 
Nuts, zincking, 471 

OERSTED, Prof., discoveries by, 
3,4 

Ohm, 22 

Ohm, law of, 4, 22-24 

proposition deduced from, 90 
Oil gutta-percha, moulding with, 635, 
636 
preparation of, 636 



INDEX. 



715 



Oil of vitriol, 669, 670 
Old brass or brush-brass finishes, 543, 
544 
gold, 432, 433 
silvering, 405 
Optical instruments, brass, black on, 

526, 527 
Organic acids, salts of, 692-694 
Orpiment, 675, 676 
Osmotic laws, value of, 50 
pressure, 49, 50 

theory of the production of the cur- 
rent, 63-65 
Ostwald, Faraday's law expressed by, 

60. 61 
Over-nickeling, 278, 279 
Oxidized silvering, 405, 406 
Oxy-acids, 41 

PACINOTTl'S ring, invention of, 7 
Paint, metallic, preparation of, 
652, 653 
Painter's gold, 416 
Palladium, deposition of, 448, 449 

properties of, 448 
Paracyanide. 336 
Parallel coupling of cells, 89 

dynamos, 172-175 
Parkes' process of metallization, 642, 

643 
Patina, 522 

artificial, 522-524 
blue-green, 524 
brown, 524 

genuine, imitation of, 523 
Patinizing, 522, 523 
Pfanhauser on reddish tinge on nickel 
anodes, 274, 275 
scattering of current- 
lines, 132, 275 
remedy for yellowish tone of nickel- 
ing by, 238 
voltametric balance of, 391-394 
Philip's process of coppering laces and 

tissues, 649, 650 
Phosphates, 46, 692 
Photo-engraving, 625-627 

-galvanography, 626, 627 
Pickling anddipping, 218-228 
objects to be silvered, 382 
Pile of Volta, 2 
Pilet's palladium bath, 449 
Pins, silvering, 503, 504 
Pipes, zincking of. 467. 468 
Pitchers, gilding inner surfaces of, 428 
Pixii, first electro-magnetic induction 

machine by, 4 
Plante's accumulator, 111, 112 



Plaster of Paris moulds for casts, 637- 
639 
rendering of, imper- 
vious, 639, 640 
Plastic objects, galvanic reproduction 

of. 634-645 
Plating, rapid, coupling cells for, 135 
room, floor in, 121, 122 
heating of, 120, 121 
light in, 119 
renewal of water in, 121 
size of, 122 

ventilation of, 119, 120 
Platinic chloride, 679, 680 
Platinizing by contact. 511 
Platinum anodes, 271. 272 

for gold baths, 421, 423 
baths, 444-446 

management of. 446 
recovery of platinum from, 448 
deposition of, 444-448 
deposits, burnishing of, 216, 217 
plating, direct, 447, 448 

execution of, 446-448 
properties of, 444 

recovery of, from platinum baths, 
448 
Plunge batteries, 84-87 
Poisoning by chemicals, 556, 557 
Polarization, 65-67 

current, appearance of. 66, 67 
electro-motive counter-force of, 130— 

132 
phenomena in nickel baths. 284, 
285 
Poles, magnetic, 10 

Polished objects, cleansing of, 217, 218 
Polishing, 206-212 

and grinding rooms, 122, 123 
deposits. 216, 217 
lathes, 208-212 
machines, automatic, 300, 301 
materials. 212, 213 
wheels, 207, 208 
Poole, Moses, first use of thermo-elec- 
tricity by. 7 
Porcelain ware, galvanoplastic decora- 
tions on, 651-656 
Positive electricity, 29 

electrode, 47 
Potash, 684 

-alum, 686 
Potassium-ammonium sulphate, 686 
and sodium, amalgams of, 4 
bitartrate, 692, 693 
carbonate, 684 

in silver baths, determination 
of, 409-411 



716 



INDEX. 



Potassium cyanide. 080-682 
as a pickle, 224 
determination of. in brass 
baths, 360, 861 
of, in copper baths, 
343-345 
first use of solntions of me- 
tallic cyanides in, 6 
handling of, 556 
poisoning by, 556 
discovery of, 3 
disulphide, electrolysis of solution 

of, 54, 55 
ferrocyanide, 683 
hydrate, 673 
nitrate, 690 
-sodium tartrate, 693 
sulphide, 674, 675 
Potential, 30 

difference of, 21 
Preece's test, 456 
Preliminary pickle, 223 
Presses, 600-602 
Pretsch, invention of heliography by, 

630 
Primary current, 16 

salts, 46 
Prime & Son, early use of a magnetic 
machine for the deposition of silver 
by ,7 
Printing plates, nickeling, 312-314 

steeling, advantage of, 477 
Proctor, Chas. H. , on electro-chemical 
cleaning, 230, 231 
on red gold solution, 
432, 433 
silver-plating the 
steel blades of 
knives, 385, 386 
Protosulphate of iron, 687 
Prussiate of silver, 683 

of zinc, 683 
Prussicacid, 670,671 

poisoning by, 556 
Pump-pistons, coppering, 656 
Pyridine in zinc baths, 461 
Pyrophosphates, 692 
Pyroxyline lacquers, 539-541 

QUADRIVALENT elements, 38 

EAIL work, interior, lacquer for, 541, 
542 
Rapid galvanoplasty, 587-593 
baths for, 590, 592 
Ratsbane, 672 
Reaction of baths, 245, 246 



Reagent papers, 42 

Raoult's method of determining the 
molecular weights of dissolved bodies, 
50,51 
Recovery of silver from old silver baths, 

412-414 
Red gilding, 430, 431 

sulphide of antimony, 675 
Reform wheel, 198 
Remanent magnetism, 13 
Reprinting, 628 
Reproduction, 558 
Residual magnetism, 13 
Resinous electricity, 29 
Resist, 507 
Resistance board, 136 
electric, unit of, 22 
of electrolyte, 128-130 
Resistances, specific, 24-26 
Retort-carbon anodes, 271 
Rieder's process of electro-engraving, 

631-634 
Ring armature, 97, 98 
Rings, plating of, with red gold, 431 
Ritter, production of secondary currents 

by, in 
Rivets, zincking, 471 
Rheostat, 136 
Rochelle salt, 693 
Rock salt, 676 

Rojas, F. Arquimedas, process for the 

production of colors on metals by 

electro-deposition invented by, 536, 

537 

Rolls of steel and cast-iron, coppering, 

656 
Rose-color gilding, 432 

gold solution, 432, 433 
Roseleur's brass baths, 350, 351, 353 
copper bath, 328, 329, 334 
metallometric balance, 388-391 
method of preparing solution of 

sodium sulphite, 501, 502 
tin bath, 450, 451, 511 
Rouge, 212 
Ruby oxide, 334 
Ruolz's bronze bath, 363 
Russell and Woolrich's brass bath, 849 

SAL AMMONIAC, 676 
Salt, common, 676 
Saltpetre, 690 
Salts, 41-45 

conducting, 249, 250 
formation of, from the acids, 44 
nomenclature of, 45, 46 
nickel, 248, 249 
of organic acids, 692-694 



INDEX. 



717 



Salzede's brass bath, 349 

Sand, H. , on agitation of baths, 238 

Sand-blast, types of, 193, 194 

Satin finish lacquer, 542 

Sawdust for drying objects, 163 

Saw-table, 618, 619 

Scamoni, improvement of heliograph y 

by, 630 
Scheele, observations by, 6 
Schneider, Wm., zinc bath recom- 
mended by, 463 
Schonbeck's galvanoplastic copper bath, 

586 
Schuckert's machine, introduction of, 8 
Schultz, O., patent of, 339 
Scissors, nickel bath for, 263 
Scratch-brush, construction of a, 191, 192 
-brushes, 189, 190 
-brushing, 189-192 
deposits, 213-215 
liquids used in, 214 
Screws, zincking, 471 
Secondary cells, 111-118 
current, 16 
salts, 46 
Sectional silver-plating, 384 
Seignette salt, 693 
Self-excitation, 97 
Separate excitation, 97 
Series coupling of dynamos, 172-175 

-wound dynamos, 103 
Shaving machines, 619, 620 
Shell, backing, 617, 618 

detaching the, from the mould, 615- 

617 
gold, 416 
Sheet-iron, nickeling, 306, 307 
zincking, 466. 467 
metal, electrolytic pickling of, 221 
steel, nickeling, 306, 307 
Sheets, iridescent, production of, 475 

large, polishing lathe for, 209 
Shunt-wound dynamos, 103-105 
Siemens' machine, introduction of, 8 
& Halske machines, introduction 
of, 8 
Silver alloys, 380, 381 

and gold, galvanoplasty in. 667, 668 
bath, coupling cells for. 133, 134 

electrolysis of a, 57 
baths, 366-370 

additions of organic substances 

to, 377-379 
agitation of, 375-377 
determination of proper pro- 
portions of silver and excess 
of potassium cyanide in, 375 
examination of, 409-412 



Silver baths, insoluble anodes in, 372 
old, recovery of silver from, 

412-414 
steel sheets as anodes for, 373 
tanks for, 370 
thickening of, 374 
treatment of. 370-375 
brown tone on, 406, 407 
calculation of time for deposition of 

determined weight of, 127 
chloride, 678, fi79 

preparation of silver bath with . 
368. 369 
cyanide, 683 

deposit, calculation of the weight 
of, from the current-strength 
used, 398-400 
heavy, baths for, 368-370 
on glass and china, 652-656 
deposition of, 365-414 
deposits, burnishing of, 216, 217 

polishing, 401 
determination of weight of deposit 

of, 386-398 
frosting, 400, 401 
galvanoplasty in, 667, 668 
in silver baths, determination of T 

411, 412 
incrustations with, 403, 404 
mat, 400 

metallized, preparation of, 652 
nitrate, 691, 692 
plating, determination of, 408 
execution of, 382-400 
ordinary, 401, 402 
sectional, 384 
properties of, 365 
recovery of, from old silver baths T 

412-414 
sheets, brushing of, 206 
Silvered articles, stripping, 407, 408 
Silvering, antique, 405 
by contact, 499. 500 
immersion, 500-504 
weight, baths for, 368-370 
cold, with paste, 504, 505 
copper wire, 403 
current-density for, 125 
mechanical and chemical prepara- 
tion of objects for, 382, 383 
nielled, 404, 405 
old, 405 

ordinary, bath for, 370 
oxidized, 405, 406 
slinging wires for, 383 
yellow tone of, 379 
Sine galvanometer, 12 
Skates, nickeling, 311 



718 



INDEX. 



Slinging wires, 160 
Smee cell, 72, 73 

Smee, Dr. Alfred, discoveries in electro- 
deposition by, 6 

experiments by, 559 
Sodium and potassium, amalgams of, 4 

bicarbonate, 08 4, 685 

bisulphite, 689, 690 

carbonate, 684 

chloride, 67G 

citrate, 694 

discovery of, 3 

hydrate, 673 

hydroxide, electrolysis of, 55, 56 

nitrate, 690 

phosphate, 692 

pyrophosphate, 692 

sulphate. 686 

sulphite, 689 

preparation of solution of, 501- 
503 
Solder, hard, removal of, from bicycle 

frames, 221, 222 
Solenoid, 15 

Solution-tension of metals. 61-63 
Solutions, theory of, 48, 49 
Solvents. 233. 234 
Sources of current, 70-118 
South pole, 10 
Specific gravity of baths, 235, 236 

resistances, 24-26 
Spencer, T. , claim by, 5 
Spoons calculation of time for deposi- 
tion of determined weight on. 127 

extra heavy coating of silver on, 
388, 381 
Spirit of nitre, 670 
Spirits of hartshorn, 673, 674 
Hpraying lacquers, 548-553 

machine, 548, 549 
Springs, coppering, 498 
Stairs, coppering parts of, 656, 657 
Stannic chloride, 677 
Stannous chloride. 677 
Steam drying barrel, 164 

sawdust box, 163 
Steel anodes for gold baths, 421-423 

baths, 475, 476 

blue on, 535 

brassing bath for, 353, 354 

cleaning of. 232 

copper baths for, 329, 330 

direct silver-plating of, 402 

galvanoplasty in, 657-661 

grinding of. 205 

gun barrels, coppering. 656 

nickeled, prevention of rusting of, 
277, 278 



Steel pens, coppering, 498 

plates, etching, 630 

rolls, coppering, 656 

sheet, nickeling, 306, 307 

sheets as anodes for silver baths, 373 

silvering, 500 

tanks, welded, 154 

tapes, zincking, 469-471 

tinning solution for, 512, 513 
Steeling, 475-477 

execution of, 477 
Steinach and Biichner's table for use of 

barium cyanide solution, 410, 411 
Stereotypes, coppering, 622, 623 

nickeling. 312-314 
Stirring contrivances. 588 
Stockmeyer's copper bath, 330 

standard formula for copper bath, 328 
Stoehrer's plunge battery, 86 
Stolba's process of nickeling, 491, 492 

tinning bath, 514 
Stoneware, coppering, 650 

tanks. 154 
Stopping-off. 402.403 
Stripping acid. 286 

defective nickeling, 285-288 

gold from gilded articles, 440, 441 

silvered articles, 407, 418 
Sugar of lead, 694 
Sulphate of iron, 687 
Sulphates. 46 

and sulphites, 6S6-690 
Sulphur combinations, 674-676 
Sulphuretted hydrogen, 674 

poisoning by, 557 
Sulphuric acid, 669, 670 

electrolysis of. 66 
Sulphurous acid, poisoning by, 557 
Snlphydrate of ammonia, 675 
Snlphydric acid, 674 
Surgical instruments, sharp, nickeling, 

310,311 
Swiss mat, 535 
Switch-boards, 180-183 
Symbols of chemical elements, 34, 36 
Synthetic chemical process, 32 
Szirmay and von Kollerich on addi- 
tions to zinc baths, 460 

TABLE for freeing objects from grease, 
161-163 
Table for inter-conversion of certain 
standard weights and meas- 
ures, 697, 698 
of bare copper wire for low volt- 
age, 702 
chemical elements with their 
symbols and atomic weights, 
35 



INDEX. 



719 



Table of content of metal in metallic 
salts, 700 
electrical resistance of pure 

copper wire, 701 
electro-chemical equivalents, 

61 
hydrometer degrees according 
to Baum£, and their weight 
by volume, 702 
resistance and conductivity of 
pure copper at different tem- 
peratures, 701 
solubilities of chemical com- 
pounds used in electro- 
technics, 698, 699 
useful numerical data, 696 
Tacks, zincking, 471 
Tampico brush, 205 
Tangent galvanometer, 12 
Tanks, 154-157 

for brass baths, 355 

galvanoplastic baths, 587 
gold baths, 421-426 
potassium-copper cyanide baths, 

335, 3^6 
silver baths, 370 
zinc baths. 465 
Tartar emetic, 693 
Tea sets, galvanoplastic decorations on, 

651 
Temperature, coefficient of, 26 

of baths, 236, 210 
Terchloride of gold, 679 
Terra-cotta objects, coppering, 650 
Thermo-electric piles, 7, 90-93 

-electricity, first use of, 7 
Thermometer degrees, conversion of 
Fahrenheit to Centigrade, and Centi- 
grade to Fahrenheit, 696 
Thermometers, coppering mercury ves- 
sels of, 651 
Thompson, Sylvanus, cobalt solution of, 

324 
Three-wire system of current-distribu- 
tion, 180 
Tin baths, 450-452 

management of, 452 
chloride, 677 
coloring, 536 
deposition of, 450-453 
deposits, polishing of, 216 
direct silvering of, 401, 402 
patina for, 533 
plate, nickeling, 306 
plating, process of, 452, 453 
properties of, 450 
salt, 677 
sepia brown tone on, 536 



Tinning by contact and by boiling, 511— 

514 
Tissues, coppering, 649, 650 
Toggle press, 600, 601 
Tombac bath, 362, 363 

cleaning of, 232, 233 

deposition of, 362, 363 

pickling of, 223, 224 
Touchstone, testing gold by, 415, 416 
Transmission, 124 
Trivalentand quinquavalent elements, 38 

elements, 38 
Trough battery, 2, 71 
Tumblers, galvanoplastic .decorations 

on, 651-656 
Tumbling barrel or drum, 194-196 
Two-polar dynamo, 96 
Type matrices, preparation of, 623 

metal, stereotypes of, nickeling, 
313,314 

UMBRELLA handles, celluloid, gal- 
vanoplastic decorations on, 656 
Union canvas wheel, 207 
Units, electric, 18-24 
Univalent elements, 38 
Universal polishing wheel, 207 

VALENCE of chemical elements, 36- 
38 
Van't Hoff, investigations of, 48, 50 
Vapor-pressure, 61 
Varrentrapp's iron bath. 475, 476 
Vases, galvanic reproduction of, 634-645 
Ventilation of plating room, 119, 120 
Verdigris, 693, 694 
Vessels, contents of, 695 
Vienna lime, 199, 212 
Villon's process of plating aluminium, 

485 
Vitreous electricity, 29 
Volt, 21 

ampere. 21 
Volta, discovery of, 2 
Voltage. low, table of bare copper wire 

for, 702 
Voltaic cell, 31 
cells, 70-84 
pile, 2 
Voltametric balance, 391-394 

controlling apparatus, 394-398 
Voltmeter, 144-147 
switch, 147-151 
Volumetric analysis, 318, 319 

determination of copper in copper 
baths, 346-348 
zinc in brass 
baths, 362 



720 



INDEX. 



WALENN'S copper bath, 335 
Walrine wheel, 208 
Warren's cobalt solution, 324, 325 
nickel and cobalt solution, 295 
Washing soda, 684 

Watch chains, plating of, with red gold, 
431 
movements, palladium bath for 
plating, 449 
Watches, graining parts of, 505-508 
Water, 233, 234 

current of, comparison of the elec- 
tric current with, 19, 20 
decomposition of. by electrolysis, 3 
-dip lacquers, 553. 554 
renewal of, in plating rooms, 121 
Watt. 21 

Watt's lead bath, 472 
Waverly voltmeter, 146, 147 
Wax compositions for moulding, 598 
melting kettles, 599 
mould, detaching deposit from. 616, 
617 
electrical contact of, 614, 615 
moulding in, 597- 00 
Weight, avoirdupois, 695 
Weights and measures, table for the 

inter-conversion of. 697 
Weill, and Newton's bronze bath, 363 

copper bath by. 334, 335 
Weston ammeter, 147 

boric acid in nickel baths, recom- 
mended by, 250 
Wheatstone's machine, introduction of, 8 
Wheels, grinding. 199, 200 

polishing, 1:07. 208 
White arsenic. 672 

prussiate of potash, 680-682 
vitriol, 688 
Wilde's machine, 7 
Wire, coppering, 498 
gilding, 4 -7-440 
nickeling, 307-309 
zincking, 469-471 
Wires', 26 

Wollaston, discovery by, 3 
Wood cuts, bath for. 590 
Wooden tanks. 155,156 
Woolrych, first magnetic machine for 

the deposition of silver by, 7 
Workshop, hygienic rules for, 555-557 
W,right, first use of solutions of the 
metallic cyanides in potassium cya- 
nide by, 6 
Wrought iron, pickling of, 218 

"VTELLOW prussiate of potash, 683 



Z ILK EN'S bath for tinning by con- 
tact, 512 
Zinc alloys, production of, 471, 472 
amalgamation of, 71,72 
anodes, 463-465 
baths, 458-463 

tanks for, 465 
black on, 531, 532 
blue-black on, 532 
brassing, bath for, 353 
bronzing on, 533 
brown patina on, 532 
carbonate, 685 
castings, brushing of, 206 
chloride, 677 

solution, electrolysis of, 67 
coloring, 531-533 
copper bath for, 333, 334 
cyanide, 683 

determination of, in brass baths, 361 
deposition of. 453-472 
etchings, nickeling. 313, 314 
gray coating on, 533 

-yellow, brown to black on, 532 
lamp-feet, nickeling of, 283 
nickel bath for, 259 
patina for, 533 
pickling of, 223 
plates, coppering, 623 
properties of, 453 
scratch-brushes for, 214 
sheet, brassing of, previous to nick- 
eling, 302, 303 

coppering of, previous to nick- 
eling, 303, 304 

freeing of, from grease, 301, 
302 

nickeled, polishing of, 305, 306 

nickeling of, 298-306 

polishing of, 206, 299, 300 
red brown shade on, 533 
sulphate. 688 
tin bath for, 451, 452 
volumetric determination of, in 

brass baths, 362 
yellow-brown shades on, 533 
Zincking by contact, 514, 515 
execution of, 465, 466 
pipes, 467, 468 
profiled objects, 468, 469 
regenerative process of, 459, 460 
screws, nuts, rivets, nails, tacks r 

etc., 471 
sheet-iron, 466, 467 
wire, 469-471 

wrought iron girders, 468, 469 
Zincography, 627-630 
Zone, neutral. 10 



The Hanson fr Van Winkle Company, Newark, N.J., U S. ./?. 



MULTIPOLAR TYPE DYNAMOS 



W/"E manufacture and are 
prepared to furnish this 
type dynamo in sizes ranging 
from 50-10,000 amperes, either 
shunt or compound wound, or 
with fields wound 
for separate exci- 
tation. We can 
absolutely recom- 
mend this type 
machine as the 
most modern and 
complete plating 
dynamo on the 
market. 

We can supply low 
voltage dynamos di- 
rect connected to a 
motor of suitable size, 
the whole outfit 
mounted on a sub- 
stantial ironsub-base. 

Motors can be fur- 
nished in any voltage 
to suit conditions. 




THE HANSON & VAN WINKLE COMPANY 

U. S. A. 
Main Office, No. 269 Oliver St. NEW YORK, CHICAGO, ILL. 

NEWARK, N. J. No. 79 Walker St. No. 108 North Clinton St. 

Canada Office, Canadian Hanson & Van Winkle Co., Limited 

Morrow Ave., Toronto, Ont. ! 



The Hanson Sr Van Winkle Company, Newark, N. J., U. S. Jf. 

The H. & V. W. 

Patented Underwriter's Rheostats 

For Electroplating Tanhs 




Made in all Sizes to suit requirements 
WE MANUFACTURE 

Multipolar Dynamos in various sizes, giving 5 and 10 volts, and ranging 
from 100 to 5,000 amperes on three-wire system, also dynamos from 50 to 
10,000 amperes on two-wire system. 

RHEOSTATS ANODES, ALL KINDS 

VOLTMETERS POLISHING MACHINERY 

AMMETERS POLISHING SUPPLIES 

CONNECTIONS POLISHING COMPOSITION, and 

Everything Used in the Plating and Polishing Shop 

Special itemized estimates furnished for complete plants. 
Write for dynamo information. 



THE HANSON & VAN WINKLE CO. 



Main Office 

No. 269 Oliver St. 

Newark, N. J. 



U. S. A. 

New York 

No. 79 Walker St. 



Chicago, 111. 
No. 108 N. Clinton St. 



Canada Office: Canadian Hanson & Van Winkle Co., Limited 
Morrow Ave., Toronto, Ont. 



The Hanson «£• Van Winkle Company, Newark, N.J., U. S. Jt. 

United States Patents June 22, 1897— February 24, 1903— Oct. 11, 1904, 

March 24, 1908 -May 19, 1908. 

Canadian Patents Nos. 58,205 and 97,852. 

Other Patents P tiding. 




The h. ca V. w. 

Mechanical E,leetro-Plating Apparatus 

Type B. Gear Drive. 

Used in Plating Nickel, Copper, Brass, Bronze, SpZinc 

These machines are particularly adapted for electro-plating quantities 
of small work in bulk, saving time, labor, and expense. They have for a 
long time been a recognized necessity in the metal manufacturing industry. 

Our patented perforated celluloid panel construction is particularly 
adapted for use with very small work. These panels are made with round 
perforations as small as T ^ in. and with oblong perforations f-x^ in. The 
celluloid being thin and tough allows for free circulation of the solution. 

We have installed over 8oo of these outfits, many of them among the 
largest and best known manufacturers in the United States and Canada, 
which are giving perfect satisfaction. 



THE HANSON & VAN WINKLE CO. 



Newark, N. J. 
269 Oliver Street 



New York 
79 Walker Street 



Chicago, 111. 
110 North Clinton St. 



Canada Office: Canadian Hanson & Van Winkle Co. 
Morrow Ave., Toronto, Ont. 



The Hanson Sr Van Winkle Company, Newark, N J ., U. S. Ji. 



WITH the advances made in 
nickel plating in the past 
years the tendency has been 
to use larger containers, which 
naturally require anodes of increas 
ed dimensions. To meet this ne- 
cessity various devices have been 
tried in the way of crowding a lar- 
ger number of plates into the tank 
or using irregular shapes, some- 
times with cumbersome attach- 
ments. After exhaustive experi- 
ments we have at last solved the 
question, and now offer to the trade 
our patented Elliptic anode. 

For many years it has been cus- 
tomary to use flat nickel Anodes, 
only because there was nothing else 
obtainable, and these flat plates are 
still in general use in many large 
establishments, which have not tak- 
en time to investigate the decided 
advantage and economy in our late 
developments. 

The patented Elliptic Anodes 
possess many points of real merit ; 
they are the result of careful ex- 
periments covering several years, 
and they overcome the disadvant- 
ages in all other shapes. 

Elliptic Anodes are 2% inches 
wide by i^ inches thick, and are 
cast in any ordinary length. 

Experience shows that all Anodes 
work more from the edges than 
from the centre, showing conclu- 
sively that circulation around the 
Anode is necessary to get the great- 
est amount of corrosion or disin- 
tegration. 




THE HANSON & VAN WINKLE CO. 

U. S. A. 
Newark, N. J. New York Chicago, 111. 

269 Oliver Street 79 Walker Street 110 North Clinton St. 

Canada Office: Canadian Hanson & Van Winkle Co. 
4 Morrow Ave., Toronto, Ont. 



The Hanson «£• Van Winkle Company, Newark, N.J., U. S. Jt. 

Electro- Galvanizing 

Cold Process. No Royalties 



Complete Outfits FurnisHed 



Samples Finished Without Charge, Estimates 
and Information Furnished On Request. 



An Economical and Practical Substitute For Hot Galvanizing 

We have fitted up a large number of plants which are operating pro- 
fitably at an increased economy over the old method. The Electro-depo- 
sition of Zinc has been attempted for many years, but within a short period 
only have practical commercial results been obtained. With the advan- 
tages secured by the use of our Compound Wound Dynamos as a source of 
current, we are now prepared to fit up complete plants for galvanizing all 
iron or steel articles, from small castings to a ship's anchor and chain. 



A PLANT FOR ELECTRO-GALVANIZING COMPRISES: 

Special Low Voltage Compound Wound Dynamo. 

Electrical Measuring Instruments. 

Llectrical Connections. 

Tank* or Tanks for Solution, with Fittings. 

Solution or Material for Solution. 

Cast Anodes of superior quality are absolutely without Waste. 

Cleaning Outfit for preparing work, including all tanks and 

supplies necessary. < 

WHEN REQUIRED WE SEND OUR EXPERT FOR 
LARGE INSTALLATIONS. 



THE HANSON & VAN WINKLE CO. 

Newark, N. J. New York Chicago, 111. 

269 Oliver Street 79 Walker Street 110 North Clinton St. 

Canada Office: Canadian Hanson & Van Winkle Co. 

Morrow Ave., Toronto, Ont. 5 



The Hanson fr Van Winkle Company, Mewark, M. J., U. S. Ji» 



Aluminum Dipping Baskets. 

We illustrate herewith our patented perforated sheet aluminum dipping 
baskets, also aluminum wire baskets which we are prepared to furnish in 
any style or shape. 



Aluminum dipping baskets are practically acid proof but must not be 
used in potash, muriatic or hydrofluoric acid. They are particularly adap- 
ted for use in washing and dipping. After a thorough test we do not hes- 
itate to recommend them. They are very light, very durable and will out- 
last the ordinary dipping baskets. 




THE HANSON & VAN WINKLE CO. 



Newark, N. J. 
269 Oliver Street 



u. s. A. 

New York 
79 Walker Street 



Chicago, 111. 
110 North Clinton St. 



Canada Office: Canadian Hanson & Van Winkle Co. 
Morrow Ave., Toronto, Ont. 



INDUSTRIAL LITERATURE 

Civilization without Diversified Industries is an Impossibility 
and all History Bears Witness to this Great Truth. H. C.B. 



CATALOGUE 

OF 

Practical and Scientific Books 

PUBLISHED BY 

Henry Carey Baird & Co. 

INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS. 

810 Walnut Street, Philadelphia. 



MS&~ Any of the Books comprised in this Catalogue will be sent by mail, 
free of postage, to any address in the world, at the publication prices. 

4Sf A Descriptive Catalogue. 94 pages, 8vo., will be sent free and free 

of postage, to any one in any part of the world, who will furnish 

his address. 

4®=* Where not otherwise stated, all of the Books in this Catalogue 
are bound in muslin. 



AMATEUR MECHANICS' WORKSHOP: 

A treatise containing plain and concise directions for the 
manipulation of Wood and Metals, including Casting, Forg- 
ing, Brazing, Soldering and Carpentry. By the author of 
the "Lathe and Its Uses." Seventh edition. Illustrated. 
8vo • $2.50 

ARLOT.— A Complete Guide for Coach Painters: 

Translated from the French of M. Arlot, Coach Painter, for 
eleven years Foreman of Painting to M. Eherler, Coach 
Maker, Paris. By A. A. Fesquet, Chemist and Engineer. 
To which is added an Appendix, containing Information re- 
specting the Materials and the Practice of Coach and Car 
Painting and Varnishing in the United States and Great 
Britain. i2mo $1.25 



2 HENRY CAREY BAIRD & CO.'S CATALOGUE 

ARMENGAUD, AMOROUX, AND JOHNSON.— The Prac- 
tical Draughtsman's Book of Industrial Design, and 
Machinist's and Engineer's Drawing Companion: 

Forming a Complete Course of Mechanical Engineering and 
Architectural Drawing. From the French of M. Armengaud 
the elder, Prof, of Design in the Conservatoire of Arts and 
Industry, Paris, and M. Armengaud the younger, and Amo- 
roux, Civil Engineers. Rewritten and arranged with addi- 
tional matter and plates, selections from and examples of 
the most useful and generally employed mechanism of the 
day. By William Johnson, Assoc. Inst. C. E. Illustrated 
by fifty folio steel plates, and fifty wood-cuts. A new edi- 
tion, 4to., cloth $5.00 

ARROWSMITH.— The Paper-Hanger's Companion: 

Comprising Tools, Pastes, Preparatory Work; Selection and 
Hanging of Wall-Papers; Distemper Painting. and Cornice- 
Tinting; Stencil Work; Replacing Sash-Cord and Broken 
Window Panes; and Useful Wrinkles and Receipts. By James 
Arrowsmith. A New, Thoroughly .Revised, and Much En- 
larged Edition. Illustrated by 25 engravings, 162 pages. 
(1905) $1.00 

ASHTON.— The Theory and Practice of the Art of Design- 
ing Fancy Cotton and Woolen Cloths from Sample: 

Giving full instructions for reducing drafts, as well as the 
methods of spooling and making out harness for cross drafts 
and finding any required reed; with calculations and tables 
of yarn. By Frederic T. Ashton, Designer, West Pittsfield, 
Mass. With fifty-two illustrations. One vol. folio $4.00 

ASKINSON. — Perfumes and and their Preparation: 

A Comprehensive Treatise on Perfumery, containing Complete 
Directions for Making Handkerchief Perfumes, Smelling- 
Salts, Sachets, Fumigating Pastils; Preparations _ for the 
Care of the Skin, the Mouth, the Hair; Cosmetics, Hair 
Dyes, and other Toilet Articles. By G. W. Askinson. 
Translated from the German by Isidor Furst. Revised by 
Charles Rice. 32 Illustrations. 8vo. $3- OQ 

BEANS. — A Treatise on Railway Curves and Location of 
Railroads: 

By E. W. Beans, C. E. Illustrated. i2mo. Morocco. .$1.00 
BELL. — Carpentry Made Easy: 

Or, The Science and Art of Framing on a New and Improved 
System. With Specific Instructions for Building Balloon 
Frames, Barn Frames, Mill Frames, Warehouses, Church 
Spires, etc. Comprising also a System of Bridge Building, 
with Bills, Estimates of Cost, and valuable Tables. Illus- 



HENRY CAREY BAIRD & CO.'S CATALOGUE 3 

trated by forty-four plates, comprising nearlv 200 figures. 
By William E. Bell, Architect and Practical Builder. 
8vo $ 5 .oo 

BERSCH.— Cellulose, Cellulose Products, and Rubber 
Substitutes: 

Comprising the Preparation of Cellulose, Parchment-Cellu- 
lose, Methods of Obtaining Sugar, Alcohol, and Oxalic Acid 
from Wood-Cellulose; Production of Nitro-Cellulose and 
Cellulose Esters; Manufacture of Artificial Silk, Viscose, 
Celluloid, Rubber Substitutes, Oil-Rubber, and Faktis. By 
Dr. Joseph Bersch. Translated by William T. Brannt. 
41 Illustrations. (1904.) $3.00 

BILLINGS.— Tobacco : 

Its History, Variety, Culture, Manufacture, Commerce, and 
Various Modes of Use. By E. R. Billings. Illustrated by 
nearly 200 engravings. 8vo $3.00 

BIRD. — The American Practical Dyers' Companion: 

Comprising a Description of the Principal Dye-Stuffs and 
Chemicals used in Dyeing, their Natures and Uses; Mor- 
dants and How Made; with the best American, English, 
French and German processes for Bleaching and Dyeing 
Silk, Wool, Cotton, Linen, Flannel, Felt, Dress Goods, Mixed 
and Hosiery Yarns, Feathers, Grass, Felt, Fur, Wool, and 
Straw Hats, Jute Yarn, Vegetable Ivory, Mats, Skins, Furs, 
Leather, etc., etc., by Wood, Aniline, and other Processes, 
together with Remarks on Finishing Agents, and Instructions 
in the Finishing of Fabrics, Substitutes for Indigo, Water- 
Proofing of Materials, Tests and Purification of Water. 
Manufacture of Aniline and other New Dye Wares, Harmoniz- 
ing Colors, etc., etc.; embracing in all over 800 Receipts for 
Colors and Shades, accompanied by 170 Dyed Samples of Raw 
Materials and Fabrics. By F. J. Bird, Practical Dyer, 
Author of "The Dyers' Hand-Book. " 8vo $4.00 

BLINN.— A Practical Workshop Companion for Tin, 
Sheet-Iron, and Copper-plate Workers: 

Containing Rules for describing various kinds of Patterns 
used by Tin, Sheet-Iron and Copper-plate Workers; Practical 
Geometry; Mensuration of Surface and Solids; Tables of the 
Weights of Metals, Lead-pipe, etc.; Tables of Areas and 
Circumferences of Circles; Japan, Varnishes, Lacquers, Ce- 
ments, Compositions, etc., etc. By Leroy J. Blinn, Master 
Mechanic. With One Hundred and Seventy Illustrations. 
l2mo $2.50 

BOOTH.— Marble Worker's Manual: 

Containing Practical Information respecting Marbles in 
general, their Cutting, Working and Polishing; Veneering of 
Marble; Mosaics; Composition and Use of Artificial Marble, 



4 HENRY CAREY BAIRD & CO.'S CATALOGUE 

Stuccos, Cements, Receipts, Secrets, etc., etc. Translated 
from the French by M. L. Booth. With an Appendix con- 
cerning American Marbles. i2mo., cloth $1.50 

BRANNT. — A Practical Treatise on Animal and Vegetable 
Fats and Oils: 

Comprising bot"h Fixed and Volatile Oils, their Physical and 
Chemical Properties and Uses, the Manner of Extracting and 
Refining them, and Practical Rules for Testing them; as well 
as the Manufacture of Artificial Butter and Lubricants, etc., 
with lists of American Patents relating to the Extraction, 
Rendering, Refining, Decomposing and Bleaching of Fats 
and Oils. By William T. Brannt, Editor of the "Techno- 
Chemical Receipt Book." Second Edition, Revised and 
in great part Rewritten. Illustrated by 302 Engravings. 
In Two Volumes. 1304 pp. 8vo $10.00 

BRANNT.— A Practical Treatise on Distillation and Rec- 
tification of Alcohol: 

Comprising Raw Materials; Production of Malt, Preparation 
of Mashes and of Yeast; Fermentation; Distillation and 
Rectification and Purification of Alcohol; Preparation of 
Alcoholic Liquors, Liqueurs, Cordials, Bitters, Fruit Essences, 
Vinegar, etc.; Examination of Materials for the Preparation 
of Malt as well as of the Malt itself; Examination of Mashes 
before and after Fermentation; Alcoholometry, with Numer- 
ous Comprehensive Tables; and an Appendix on the Manu- 
facture of Compressed Yeast and the Examination of Alcohol 
and Alcoholic Liquors for Fusel Oil and other Impurities. 
By William T. Brannt, Editor of "The Techno-Chemical 
Receipt Book." Second Edition. Entirely Rewritten. 
Illustrated by 105 engravings. 460 pages, 8vo. (Dec, 
1903) $12.50 

BRANNT.— India Rubber, Gutta-Percha and Balata: 

Occurrence, Geographical Distribution, and Cultivation, Ob- 
taining and Preparing the Raw Materials, Modes of Working 
and Utilizing them, including Washing, Maceration, Mixing, 
Vulcanizing, Rubber and Gutta-Percha Compounds, Utiliza- 
tion of Waste, etc. By William T. Brannt. Illustrated. 
i2mo. A new edition in preparation. 

BRANNT. — A Practical Treatise on the Manufacture of 
Vinegar and Acetates, Cider, and Fruit- Wines: 

Preservation of Fruits and Vegetables by Canning and Evap- 
oration; Preparation of Fruit-Butters, Jellies, Marmalades, 
Catchups, Pickles, Mustards, etc. Edited from various 
sources. By William T. Brannt. Illustrated by 79 En- 
gravings. 479 pp. 8vo (Scarce) 

BRANNT.— The Metallic Alloys: A Practical Guide 

For the Manufacture of all kinds of Alloys, Amalgams, and 
Solders, used by Metal Workers: together with their Chemical 



HENRY CAREY BAIRD & CO.'S CATALOGUE 5 

•_ 

and Physical Properties and their Application in the Arts 
and the Industries; with an Appendix on the Coloring of 
Alloys and the Recovery of Waste Metals. By William 
T. Brannt. 45 Engravings. Third, Revised, and Enlarged 
Edition. 570 pages. 8vo Net, $5.00 

BRANNT.— The Metal Worker's Handy-Book of Receipts 
and Processes: 

Being a Collection of Chemical Formulas and Practical 
Manipulations for the working of all Metals; including the 
Decoration and Beautifying of Articles Manufactured there- 
from, as well as their Preservation. Edited from various 
sources. By William T. Brannt. Illustrated. i2mo. .$2.50 

BRANNT.— Petroleum : 

Its History, Origin, Occurrence, Production, Physical and 
Chemical Constitution, Technology, Examination and Uses; 
Together with the Occurrence and Uses of Natural Gas. 
Edited chiefly from the German of Prof. Hans Hoefer and Dr. 
Alexander Veith, by Wm. T. Brannt. Illustrated by 3 
Plates and 284 Engravings. 743 pp. 8vo $12.50 

BRANNT.— The Practical Dry Cleaner, Scourer and 
Garment Dyer: 

Comprising Dry, Chemical, or French Cleaning; Purifica- 
tion of Benzine; Removal of Stains, or Spotting; Wet Clean- 
ing; Finishing Cleaned Fabrics; Cleaning and Dyeing Furs, 
Skin Rugs and Mats; Cleaning and Dyeing Feathers; Clean- 
ing and Renovating Felt, Straw and Panama Hats; Bleach- 
ing and Dyeing Straw and Straw Hats; Cleaning and Dyeing 
Gloves; Garment Dyeing; Stripping, Analysis of Textile 
Fabrics. Edited by William T. Brannt, Editor of "The 
Techno-Chemical Receipt Book." Fourth Edition, Revised 
and Enlarged. Illustrated by Forty-One Engravings. 12 
mo. 371 pp $2.50 

CONTENTS: I. Dry Chemical or French Cleaning. II. Removal of 
Stains, or Spotting. III. Wet Washing. IV. Finishing Cleaned Fabrics. V. 
Cleaning and Dyeing Furs, Skin Rugs and Mats. VI. Cleaning and Dye- 
ing Feathers. VII. Cleaning and Renovating Felt, Straw and Panama 
Hats; Bleaching and Dyeing Straw and Straw Hats. VIII. Cleaning and 
Dyeing Gloves. IX. Garment Dyeing. X. Stripping Colors from Gar- 
ments and Fabrics. XI. Analysis of Textile Fabrics. Index. 

BRANNT.— The Soap Maker's Hand-Book of Materials 

Processes and Receipts for every description of Soap includ- 
ing Fats, Fat Oils and Fatty Acids; Examination of Fats and 
Oils; Alkalies; Testing Soda and Potash; Machines and 
Utensils; Hard Soaps; Soft Soaps; Textile Soaps; Washing 
Powders and Allied Products; Toilet Soaps, Medicated 
Soaps, and Soap Specialties; Essential Oils and other Perfum- 
ing Materials; Testing Soaps. Edited chiefly from the 
German of Dr. C. Deite, A. Engelhardt, F. Wiltner, 



^ HENRY CAREY BAIRD & CO.'S CATALOGUE 

and numerous other Experts. With Additions by William 
T. Brannt, Editor of " The Techno-Chemical Receipt Book." 
Illustrated by Fifty-Four Engravings. Second edition, Re- 
vised and in great part Re- Written. 535 pp. 8vo $6.00 

BRANNT. — Varnishes, Lacquers, Printing Inks and Seal- 
ing Waxes: 

Their Raw Materials and their Manufacture, to which is 
added the Art of Varnishing and Lacquering, including the 
Preparation of Putties and of Stains for Wood, Ivory, Bone, 
Horn, and Leather. By William T. Brannt. Illustrated 
by 39 Engravings, 338 pages. i2mo $3.00 

BRANNT— WAHL.— The Techno-Chemical Receipt Book: 

Containing several thousand Receipts covering the latest, 
most important, and most useful discoveries in Chemical 
Technology, and their Practical Application in the Arts and 
the Industries. Edited chiefly from the German of Drs. 
Winckler, Eisner, Heintze, Mierzinski, Jacobsen, Koller and 
Heinzerling, with additions by Wm. T. Brannt and Wm. H. 
Wahl, Ph. D. Illustrated by 78 engravings. i2mo. 495 
pages $2.00 

BROWN. — Five Hundred and Seven Mechanical Move- 
ments: 

Embracing all those which are most important in Dynamics, 
Hydraulics, Hydrostatics, Pneumatics, Steam Engines, Mill 
and other Gearing, Presses, Horology, and Miscellaneous 
Machinery; and including many movements never before 
published, and several of which have only recently come into 
use. By Henry T. Brown $1.00 

BULLOCK.— The Rudiments of Architecture and Build- 
ing: 

For the use of Architects, Builders, Draughtsmen, Machin- 
ists, Engineers and Mechanics. Edited by John Bullock, 
author of "The American Cottage Builder." Illustrated 
by 250 Engravings. 8vo. $2.50 

BYRNE. — Hand-Book for the Artisan, Mechanic, and 
Engineer : 

Comprising the Grinding and Sharpening of Cutting Tools, 
Abrasive Processes, Lapidary Work, Gem and Glass En- 
graving, Varnishing and Lacquering, Apparatus, Materials 
and Processes for Grinding and Polishing, etc. By Oliver 
Byrne. Illustrated by 185 wood engravings. 8vo $4.00 

BYRNE.— Pocket-Book for Railroad and Civil Engineers: 

Containing New, Exact and Concise Methods for Laying out 
Railroad Curves, Switches, Frog Angles and Crossings; the 
Staking out of work; Levelling; the Calculation of Cuttings; 
Embankments; Earthwork, etc. By Oliver Byrne. i8mo., 
full bound, pocketbook form $1.50 



HENRY CAREY BAIRD & CO.'S CATALOGUE 7 

BYRNE.— The Practical Metal-Worker's Assistant: 

Comprising Metallurgic Chemistry; the Arts of Working all 
Metals and Alloys; Forging of Iron and Steel; Hardening and 
Tempering; Melting and Mixing; Casting and Founding; 
Works in Sheet Metals; the Process Dependent on the Duc- 
tility of the Metals; Soldering; etc. By John Percy. The 
Manufacture of Malleable Iron Castings, and Improvements 
in Bessemer Steel. By A. A. Fesquet, Chemist and En- 
gineer. With over Six Hundred Engravings, Illustrating 
every Branch of the Subject. 8vo $3-5° 

CABINET MAKER'S ALBUM OF FURNITURE: 

Comprising a Collection of Designs for various Styles of 
Furniture. Illustrated by Forty-eight Large and Beau- 
tifully Engraved Plates. Oblong, 8vo $1-5° 

CALLINGHAM.— Sign Writing and Glass Embossing: 

A complete Practical Illustrated Manual of the Art. By 
James Callingham. To which are added Numerous Alpha- 
bets and the Art of Letter Painting Made Easy. By James 
C. Badenoch. 258 pages. i2mo $1.5° 

CAREY.— A Memoir of Henry C. Carey: 

By Dr. Wm. Elder. With a portrait. 8vo., cloth 75 

CAREY.— The Works of Henry C. Carey: 

Manual of Social Science. Condensed from Carey's 
"Principles of Social Science." By Kate McKean. i vol. 
i2mo $2.00 

Miscellaneous Works. With a Portrait. 2 vols. 8vo. $10.00 

Past, Present and Future. 8vo $2.50 

Principles of Social Science. 3 volumes, 8vo $10.00 

The Slave-Trade, Domestic and Foreign; Why it Exists, 

and How it may be Extinguished (1853). 8vo $2.00 

The Unity of Law: As Exhibited in the Relations of Phys- 
ical, Social, Mental and Moral Science (1872). 8vo $2.50 

COOLEY. — A Complete Practical Treatise on Perfumery: 

Being a Hand-book of Perfumes, Cosmetics and other Toilet 
Articles, with a Comprehensive Collection of Formula?. By 
Arnold Cooley. i2mo $1.00 

COURTNEY.— The Boiler Maker's Assistant in Drawing, 
Templating, and Calculating Boiler Work and Tank 
Work, etc. 

Revised by D. K. Clark. 102 ills. Fifth edition 80 

COURTNEY.— The Boiler Maker's Ready Reckoner: 

With Examples of Practical Geometry and Templating. Re- 
vised by D. K. Clark, C. E. 37 illustrations. Fifth edi- 
tion $i-6o 



8 HENRY CAREY BAIRD & CO.'S CATALOGUE 

CRISTIANL— A Technical Treatise on Soap and Candles: 

With a Glance at the Industry of Fats and Oils. By R. S. 
Cristiani, Chemist. Author of "Perfumery and Kindred 
Arts." Illustrated by 176 engravings. 581 pages, 8vo. .$15.00 

CROSS.— The Cotton Yarn Spinner: 

Showing how the Preparation should be arranged for Differ- 
ent Counts of Yarns by a System more uniform than has hith- 
erto been practiced; by having a Standard Schedule from 
which we make all our Changes. By Richard Cross. 122 
pp. i2mo 75 

DAVIDSON.— A Practical Manual of House Painting, 
Graining, Marbling, and Sign-Writing: 

Containing full information on the processes of House Paint- 
ing in Oil and Distemper, the Formation of Letters and 
Practice of Sign-Writing, the Principles of Decorative Art, 
a Course of Elementary Drawing for House Painters, Writers, 
etc., and a Collection of Useful Receipts. With nine colored 
illustrations of Woods and Marbles, and numerous wood en- 
gravings. By Ellis A. Davidson. i2mo $2.00 

DAVIES. — A Treatise on Earthy and Other Minerals and 
Mining: 

By D. C. Davies, F. G. S., Mining Engineer, etc. Illustrated 
by 76 Engravings. i2mo $5.00 

DAVIES. — A Treatise on Metalliferous Minerals and 
Mining : 

By D. C. Davies, F. G. S., Mining Engineer, Examiner of 
Mines, Quarries and Collieries. Illustrated by 148 engrav- 
ings of Geological Formations, Mining Operations and Ma- 
chinery, drawn from the practice of all parts of the world. 
Fifth Edition, thoroughly Revised and much Enlarged by 
his son, E. Henry Davies. i2mo. 524 pages $5-00 

DAVIS. — A Practical Treatise on the Manufacture of 
Brick, Tiles and Terra-Cotta: 

Including Stiff Clay, Dry Clay, Hand Made, Pressed or Front, 
and Roadway Paving Brick, Enamelled Brick, with Glazes 
and Colors, Fire Brick and Blocks, Silica Brick, Carbon Brick, 
Glass Pots, Retorts, Architectural Terra-Cotta, Sewer Pipe, 
Drain Tile, Glazed and Unglazed Roofing Tile, Art Tile, Mosaics, 
and Imitation of Intarsiaor Inlaid Surfaces. Comprising every 
product of Clay employed in Architecture, Engineering, and 
the Blast Furnace. With a Detailed Description of the Differ- 
ent Clays employed, the Most Modern Machinery, Tools, 
and Kilns used, and the Processes for Handling, Disintegrat- 
ing, Tempering, and Moulding the Clay into Shape, Drying, 
Setting, and Burning. By Charles Thomas Davis. Third 
Edition. Revised and in great part rewritten. Illustrated 
by 261 engravings. 662 pages (Scarce.) 



HENRY CAREY BAIRD & CO.'S CATALOGUE 9 

DAVIS.— The Manufacture of Paper: 

Being a Description of the various Processes for the Fabrica- 
tion, Coloring and Finishing of every kind of Paper, Includ- 
ing the Different Raw Materials and the Methods for De- 
termining their Values, the Tools, Machines and Practical 
Details connected with an intelligent and a profitable prose- 
cution of the art, with special reference to the best American 
Practice. To which are added a History of Paper, complete 
Lists of Paper-Making Materials, List of American Machines, 
Tools and Processes used in treating the Raw Materials, and 
in Making, Coloring and Finishing Paper. By Charles T. 
Davis. Illustrated by 156 Engravings. 608 pages. 8vo. 

$6.00 

DAWIDOWSKY— BRANNT.— A Practical Treatise on the 
Raw Materials and Fabrication of Glue, Gelatine, 
Gelatine Veneers and Foils, Isinglass, Cements, 
Pastes, Mucilages, etc.: 

Based upon Actual Experience. By F. Dawidowsky, Tech- 
nical Chemist. Translated from the German, with extensive 
additions, including a description of the most Recent American 
Processes, by William T. Brannt. 2d revised edition, 350 
pages. (1905.) Price $3.00 

DEITE. — A Practical Treatise on the Manufacture of 
Perfumery : 

Comprising directions for making all kinds of Perfumes, 
Sachet Powders, Fumigating Materials, Dentifrices, Cos- 
metics, etc., with a full account of the Volatile Oils, Balsams, 
Resins, and other Natural and Artificial Perfume-substances, 
including the Manufacture of Fruit Ethers, and tests of their 
purity. By Dr. C. Deite, assisted by L. Borchert, F. 
Eichbaum, E. Kugler, H. Toeffner, and other experts. 
From the German, by Wm. T. Brannt. 28 Engravings. 
358 pages. 8vo $3.00 

DE KONINCK— DIETZ.— A Practical Manual of Chemical 
Analysis and Assaying: 

As applied to the Manufacture of Iron from its Ores, and to 
Cast Iron, Wrought Iron, and Steel, as found in Commerce. 
By L. L. DeKoninck, Dr. Sc, and E. Dietz, Engineer. Ed- 
ited with Notes, by Robert Mallet, F. R. S., F. S. G., M. 
I. C. E., etc. American Edition, Edited with Notes and an 
Appendix on Iron Ores, by A. A. Fesquet, Chemist and 
Engineer. i2mo $1.00 

DIETERICHS.— A Treatise on Friction, Lubrication, 
Oils and Fats: 

The Manufacture of Lubricating Oils, Paint Oils, and of 
Grease, and the Testing of Oils. By E. F. Dieterichs, 



io HENRY CAREY BAIRD & CO.'S CATALOGUE 

Member of the Franklin Institute; Member National Associa- 
tion of Stationary Engineers; Inventor of Dieterichs' Valve- 
Oleum Lubricating Oils. i2mo. (1906.) A practical book 
by a practical man $1.25 

DUNCAN. — Practical Surveyor's Guide: 

Containing the necessary information to make any person of 
common capacity, a finished land surveyor, without the aid 
of a teacher. By Andrew Duncan. Revised. 72 Engrav- 
ings. 214 pp. i2mo $1.50 

DUPLAIS. — A Treatise on the Manufacture and Dis- 
tillation of Alcoholic Liquors: 

Comprising Accurate and Complete Details in Regard to 
Alcohol from Wine, Molasses, Beets, Grain, Rice, Potatoes, 
Sorghum, Asphodel, Fruits, etc.; with the Distillation and 
Rectification of Brandy, Whiskey, Rum, Gin, Swiss Absinthe, 
etc., the Preparation of Aromatic Waters, Volatile Oils or 
Essences, Sugars, Syrups, Aromatic Tinctures, Liqueurs, 
Cordial Wines, Effervescing Wines, etc., the Ageing of Brandy 
and the improvement of Spirits, with Copious Directions 
and Tables for Testing and Reducing Spirituous Liquors, etc., 
etc. Translated and Edited from the French of MM. Du- 
plais. By M. McKennie, M. D. Illustrated. 743 pp. 
8vo $15.00 

EDWARDS.— A Catechism of the Marine Steam-Engine: 

For the use of Engineers, Firemen, and Mechanics. A Prac- 
tical Work for Practical Men. By Emory Edwards, Me- 
chanical Engineer. Illustrated by sixty-three Engravings, 
including examples of the most modern Engines. Third 
edition, thoroughly revised, with much additional matter. 
i2mo. 414 pages $1.50 

EDWARDS. — American Marine Engineer, Theoretical 
and Practical: 

With Examples of the latest and most approved American 
Practice. By Emory Edwards. 85 Illustrations. i2mo. 

$1.50 

EDWARDS. — Modern American Locomotive Engines: 

Their Design, Construction and Management. By Emory 
Edwards. Illustrated. i2mo $1.50 

EDWARDS. — 900 Examination Questions and Answers: 

For Engineers and Firemen (Land and Marine) who desire 
to obtain a United States Government or State License. 
Pocket-book form, gilt edge $1.50 

EDWARDS.— The American Steam Engineer: 

Theoretical and Practical, with examples of the latest and 
most approved American practice in the design and con- 
struction of Steam Engines and Boilers. For the use of 



HENRY CAREY BAIRD & CO.'S CATALOGUE n 

Engineers, machinists, boiler-makers, and engineering stu- 
dents. By Emory Edwards. Fully illustrated. 419 pages. 
i2mo $1.50 

EDWARDS.— The Practical Steam Engineer's Guide: 

In the Design, Construction, and Management of American 
• Stationary, Portable, and Steam Fire-Engines, Steam Pumps, 
Boilers, Injectors, Governors, Indicators, Pistons and Rings, 
Safety Valves and Steam Gauges. For the use of Engineers, 
Firemen, and Steam Users. By Emory Edwards. Illus- 
trated by 119 engravings. 420 pages. i2mo $2.00 

ELDER. — Conversations on the Principal Subjects of 
Political Economy: 
By Dr. William Elder. 8vo $i-5° 

ELDER.— Questions of the Day: 

Economic and Social. By Dr. William Elder. 8vo. $3.00 

ERNI AND BROWN.— Mineralogy Simplified: 

Easy Methods of Identifying Minerals, including Ores, by 
Means of the Blow-pipe, by Flame Reactions, by Humid 
Chemical Analysis, and by Physical Tests. By Henri 
Erni, A. M., M. D. Fourth Edition, revised, re-arranged 
and with the addition of entirely new matter, including Tables 
for the Determination of Minerals by Chemicals and Pyrog- 
nostic Characters, and by Physical Characters. By Amos 
P. Brown, E. M., Ph. D. 464 pp. Illustrated by 123 En- 
gravings, pocket-book form, full flexible morocco, gilt edges. 

$2.50 

FAIRBAIRN. — The Principles of Mechanism and Machi- 
nery of Transmission: 

Comprising the Principles of Mechanism, Wheels, and Pul- 
leys, Strength and Proportion of Shafts, Coupling of Shafts, 
and Engaging and Disengaging Gear. By Sir William 
Fairbairn, Bart., C. E. Beautifully illustrated by over 150 
wood-cuts. In one volume, i2mo $2.00 

FLEMING. — Narrow Gauge Railways in America: 

A Sketch of their Rise, Progress, and Success. Valuable 
Statistics as to Grades, Curves, Weight of Rail, Locomotives, 
Cars, etc. By Howard Fleming. Illustrated. 8vo. ..$1.00 

FLEMMING.— Practical Tanning: 

A Handbook of Modern Processes, Receipts, and Sugges- 
tions for the Treatment of Hides, Skins, and Pelts of Every 
Description. By Lewis A. Flemming, American Tanner. 
630 pp. 8vo. 1910 $6.00 

FORSYTH.— Book of Designs for Headstones, Mural, and 
other Monuments: 

Containing 78 Designs. By James Forsyth, With an In- 
troduction by Charles Boutell, M. A. 4to. Cloth.. .$3.00 



12 HENRY CAREY BAIRD & CO.'S CATALOGUE 

GARDNER.— Everybody's Paint Book: 

A Complete Guide to the Art of Outdoor and Indoor Paint- 
ing. 38 illustrations. l2mo. 183 pp $1.00 

GARDNER.— The Painter's Encyclopaedia : 

Containing Definitions of all Important Words in the Art of 
Plain and Artistic Painting, with Details of Practice in Coach, 
Carriage, Railway Car, House, Sign, and Ornamental Paint- 
ing, including Graining, Marbling, Staining, Varnishing, 
Polishing, Lettering, Stenciling, Gilding, Bronzing, etc. By 
Franklin B. Gardner. 158 illustrations. i2mo. 427 pp. 

$2.00 

GEE.— The Goldsmith's Handbook: 

Containing full instructions for the Alloying and Working of 
Gold, including the Art of Alloying, Melting, Reducing, Color- 
ing, Collecting, and Refining; the Processes of Manipulation, Re- 
covery of Waste; Chemical and Physical Properties of Gold; 
with a New System of Mixing its Alloys; Solders, Enamels^ 
and other Useful Rules and Recipes. By George E. Gee. 
i2mo $1.25 

GEE. — The Jeweler's Assistant in the Art of Working in 
Gold: 

A Practical Treatise for Masters and Workmen. l2mo. $3.00 

GEE.— The Silversmith's Handbook: 

Containing full instructions for the Alloying and Working of 
Silver, including the different modes of Refining and Melting 
the Metal; its Solders; the Preparation of Imitation Alloys; 
Methods of Manipulation; Prevention of Waste; Instructions 
for Improving and Finishing the Surface of the Work; together 
with other Useful Information and Memoranda. By George 
E. Gee. Illustrated. i2mo $1.25 

GOTHIC ALBUM FOR CABINET-MAKERS: 

Designs for Gothic Furniture. Twenty-three plates. Ob- 
long $1.00 

GRANT.— A Handbook on the Teeth of Gears: 

Their Curves, Properties, and Practical Construction. By 
George B. Grant. Illustrated. Third Edition, enlarged. 
8vo $1.00 

GREGORY.— Mathematics for Practical Men: 

Adapted to the Pursuits of Surveyors, Architects, Mechan- 
ics, and Civil Engineers. By Olinthus Gregory. 8vo., 
plates $3.00 

GRISWOLD. — Railroad Engineer's Pocket Companion 
for the Field: 

Comprising Rules for Calculating Deflection Distances and 
Angles, Tangential Distances and Angles and all Necessary 
Tables for Engineers; also the Art of Levelling from Prelim- 



HENRY CAREY BAIRD & CO.'S CATALOGUE 13 

inary Survey to the Construction of Railroads, intended 
Expressly for the Young Engineer, together with Numerous 
Valuable Rules and Examples. By W. Griswold. i2mo. 
pocketbook form $1.50 

GRUNER. — Studies of Blast Furnace Phenomena: 

By M. L. Gruner, President of the General Council of Mines 
of France, and lately Professor of Metallurgy at the Ecole des 
Mines. Translated, with the author's sanction, with an Ap- 
pendix, by L. D. B. Gordon, F. R. S. E., F. G. S. 8vo. $2.50 

Hand-Book of Useful Tables for the Lumberman, Farmer 
and Mechanic: 

Containing Accurate Tables of Logs Reduced to Inch Board 
Measure, Plank, Scantling and Timber Measure; Wages and 
Rent, by Week or Month; Capacity of Granaries, Bins and 
Cisterns; Land Measure, Interest Tables with Directions 
for finding the Interest on any sum at 4, 5, 6, 7 and 8 per cent., 
and many other Useful Tables. 32mo., boards. 186 pages. 

•25 

HASERICK.— The Secrets of the Art of Dyeing Wool, 
Cotton and Linen: 

Including Bleaching and Coloring Wool and Cotton Hosiery 
and Random Yarns. A Treatise based on Economy and 
Practice. By E. C. Haserick. Illustrated by 323 Dyed 
Patterns of the Yarns or Fabrics. 8vo $4-50 

HATS AND FELTING: 

A Practical Treatise on their Manufacture. By a Practical 
Hatter. Illustrated by Drawings of Machinery, etc. 8vo. 

$1.00 

HAUPT. — A Manual of Engineering Specifications and 
Contracts : 

By Lewis M. Haupt, C. E. Illustrated with numerous 
maps. 328 pp. 8vo $2.00 

HAUPT.— Street Railway Motors: 

With Descriptions and Cost of Plants and Operation of the 
Various Systems now in Use. i2mo $1.50 

HAUPT.— The Topographer, His Instruments and Meth- 
ods. 

By Lewis M. Haupt, A. M., C. E. Illustrated with numer- 
ous plates, maps and engravings. 247 pp. 8vo $2.00 

HULME. — Worked Examination Questions in Plane 
Geometrical Drawing: 

For the Use of Candidates for the Royal Military Academy, 
Woolwich; the Royal Military College, Sandhurst; the In- 
dian Civil Engineering College, Cooper's Hill; Indian Public 
Works and Telegraph Department; Royal Marine Light In- 



14 HENRY CAREY BAIRD & CO.'S CATALOGUE 

fantry; the Oxford and Cambridge Local Examinations, etc. 
By F. Edward Hulme, F. L. S., F. S. A., Art-Master Marl- 
borough College. Illustrated by 300 examples. Small 
quarto $1.00 

KELLEY. — Speeches, Addresses, and Letters on Industrial 
and Financial Questions: 

By Hon. William D. Kelley, M. C. 544 pages. 8vo. $2.00 

KEMLO.— Watch-Repairer's Hand-Book: 

Being a Complete Guide to the Young Beginner, in Taking 
Apart, Putting Together, and Thoroughly Cleaning the 
English Lever and other Foreign Watches, and all American 
Watches. By F. Kelmo, Practical Watchmaker. With Il- 
lustrations. i2mo $1.25 

KICK. — Flour Manufacture: 

A Treatise on Milling Science and Practice. By Frederick 
Kick, Imperial Regierungsrath, Professor of Mechanical 
Technology in the Imperial German Polytechnic Institute, 
Prague. Translated from the second enlarged and revised 
edition with supplement by H. H. P. Powles, Assoc. Memb. 
Institution of Civil Engineers. Illustrated with 28 Plates, 
and 167 Wood-cuts. 367 pages. 8vo $10.00 

KINGZETT.— The History, Products, and Processes of 
the Alkali Trade: 

Including the most Recent Improvements. By Charles 
Thomas Kingzett, Consulting Chemist. With 23 illustra- 
tions. 8vo $2.00 

KIRK. — A Practical Treatise on Foundry Irons: 

Comprising Pig Iron, and Fracture Grading of Pig and Scrap 
Irons; Scrap Irons; Mixing Irons; Elements and Metalloids: 
Grading Iron by Analysis; Chemical Standards for Iron 
Castings; Testing Cast Iron; Semi-Steel; Malleable Iron; 
Etc., Etc. By Edward Kirk, Practical Moulder and Melter, 
Consulting Expert in Melting. Illustrated. 294 pages. 
8vo. 191 1 $3.00 

KIRK.— The Cupola Furnace: 

A Practical Treatise on the Construction and Management of 
Foundry Cupolas. By Edward Kirk, Practical Moulder and 
Melter, Consulting Expert in Melting. Illustrated by 106 
engravings. Third Edition, revised and enlarged. 482 
pages. 8vo. 1910 $3.50 

KOENIG.— Chemistry Simplified: 

A Course of Lectures on the Non-Metals, Based upon the 
Natural Evolution of Chemistry. Designed Primarily for 
Engineers. By George Augustus Koenig, Ph. D., A. M., 
E. M., Professor of Chemistry, Michigan College of Mines, 
Houghton. Illustrated by 103 Original Drawings. 449 pp. 
i2mo. (1906) $2.25 



HENRY CAREY BAIRD & CO.'S CATALOGUE 15 

LANGBEIN.— A Complete Treatise on the Electro-Deposi- 
tion of Metals: 

Comprising Electro-Plating and Galvanoplastic Operations, 
the Deposition of Metals by the Contact and Immersion Pro- 
cesses, the Coloring of Metals, the Methods of Grinding and 
Polishing, as well as the Description of the Voltaic Cells, 
Dynamo-Electric Machines, Thermopiles, and of the Materi- 
als and Processes Used in Every Department of the Art. 
Translated from the Fifth German Edition of Dr. George 
Langbein, Proprietor of a Manufactory for Chemical Pro- 
ducts, Machines, Apparatus and Utensils for Electro-Platers, 
and of an Electro-Plating Establishment in Leipzig. With 
Additions by William T. Brannt, Editor of "The Techno- 
Chemical Receipt Book." Sixth Edition, Revised and En- 
larged. Illustrated by 163 Engravings. 8vo. 725 pages. 
(1909.) $5-oo 

LARKIN. — The Practical Brass and Iron Founder's 
Guide : 

A Concise Treatise on Brass Founding, Moulding, the Metals 
and their Alloys, etc.; to which are added Recent Improve- 
ments in the Manufacture of Iron, Steel by the Bessemer 
Process, etc., etc. By James Larkin, late Conductor of the 
Brass Foundry Department in Reany, Neafie & Co.'s Penn 
Works, Philadelphia. New edition, revised, with extensive 
additions. 414 pages. i2mo $2.50 

LEHNER.— The Manufacture of Ink: 

Comprising the Raw Materials, and the Preparation of 
Writing, Copying and Hektograph Inks, Safety Inks, Ink 
Extracts and Powders, etc. Translated from the German 
of Sigmund Lehner, with additions by William T. Brannt. 
Illustrated. i2mo $2.00 

LEROUX. — A Practical Treatise on the Manufacture of 
Worsteds and Carded Yarns: 

Comprising Practical Mechanics, with Rules and Calcula- 
tions applied to Spinning; Sorting, Cleaning, and Scouring 
Wools; the English and French Methods of Combing, Draw- 
ing, and Spinning Worsteds, and Manufacturing Carded 
Yarns. Translated from the French of Charles Leroux, 
Mechanical Engineer and Superintendent of a Spinning-Mill, 
by Horatio Paine, M. D., and A. A. Fesquet, Chemist and 
Engineer. Illustrated by twelve large Plates. 8vo $3.00 

LESLIE.— Complete Cookery: 

Directions for Cookery in its Various Branches. By Miss 
Leslie. Sixtieth thousand. Thoroughly revised, with the 
additions of New Receipts. i2mo $1.00 

LE VAN.— The Steam Engine and the Indicator: 

Their Origin and Progressive Development; including the 
Most Recent Examples of Steam and Gas Motors, together 



16 HENRY CAREY BAIRD & CO.'S CATALOGUE 

with the Indicator, its Principles, its Utility, and its Applica- 
tion. By William Barnet Le Van. Illustrated by 205 
Engravings, chiefly of Indicator-Cards. 469 pp. 8vo. $2.00 

LIEBER.— Assayer's Guide: 

Or, Practical Directions to Assayers, Miners, and Smelters, 
for the Tests and Assays, by Heat and by Wet Processes, for 
the Ores of all the principal Metals, of Gold and Silver Coins 
and alloys, and of Coal, etc. By Oscar M. Lieber. Re- 
vised. 283 pp. i2mo $1 .50 

Lockwood's Dictionary of Terms: 

Used in the Practice of Mechanical Engineering, embracing 
those Current in the Drawing Office, Pattern Shop, Foundry, 
Fitting, Turning, Smith's and Boiler Shops, etc., etc., com- 
prising upwards of Six Thousand Definitions. Edited by a 
Foreman Pattern Maker, author of "Pattern Making." 417 
pp. i2mo $3.75 

LUKIN.— The Lathe and Its Uses: 

Or Instruction in the Art of Turning Wood and Metal. In- 
cluding a Description of the Most Modern Appliances for the 
Ornamentation of Plane and Curved Surfaces, an Entirely 
Novel Form of Lathe for Eccentric and Rose-Engine Turning; 
A Lathe and Planing Machine Combined; and Other Valu- 
able Matter Relating to the Art. Illustrated by 462 engrav- 
ings. Seventh edition. 315 pages. 8vo $4.25 

MAUCHLINE.— The Mine Foreman's Hand-Book: 

Of Practical and Theoretical Information on the Opening, 
Ventilating, and Working of Collieries. Questions and An- 
swers on Practical and Theoretical Coal Mining. Designed 
to Assist Students and Others in Passing Examinations for 
Mine Foremanships. By Robert Mauchline. 3d Edi- 
tion. Thoroughly Revised and Enlarged by F. Ernest 
Brackett. 134 engravings. 8vo. 378 pages. (1905.) $3.75 

MOLESWORTH.— Pocket-Book of Useful Formulae and 
Memoranda for Civil and Mechanical Engineers. 

By Guilford L. Molesworth, Member of the Institution of 
Civil Engineers, Chief Resident Engineer of the Ceylon 
Railway. Full-bound in Pocketbook form $1.00 

MOORE. — The Universal Assistant and the Complete 
Mechanic- 
Containing over one million Industrial Facts, Calculations, 
Receipts, Processes, Trades Secrets, Rules, Business Forms, 
Legal Items, etc., in every occupation, from the Household 
to the Manufactory. By R. Moore. * Illustrated by 500 
Engravings. i2mo $2.50 



HENRY CAREY BAIRD & CO.'S CATALOGUE 17 

NAPIER. — A System of Chemistry Applied to Dyeing: 

By James Napier, F. C. S. A New and Thoroughly Revised 
Edition. Completely brought up to the present state of the 
Science, including the Chemistry of Coal Tar Colors, by A. 
A. Fesquet, Chemist and Engineer. With an Appendix on 
Dyeing and Calico Printing, as shown at the Universal Ex- 
position, Paris, 1867. Illustrated. 8vo. 422 pages. . .$2.00 

NICHOLLS.— The Theoretical and Practical Boiler-Maker 
and Engineer's Reference Book: 

Containing a variety of Useful Information for Employers 
of Labor, Foremen and Working Boiler-Makers, Iron, 
Copper, and Tinsmiths, Draughtsmen, Engineers, the Gen- 
eral Steam-using Public, and for the Use of Science Schools 
and classes. By Samuel Nicholls. Illustrated by sixteen 
plates. i2mo $2.50 

NICHOLSON.— A Manual of the Art of Bookbinding: 

Containing full instructions in the different Branches of For- 
warding, Gilding, and Finishing. Also, the Art of Marbling 
Book-edges and Paper. By James B. Nichollson. Il- 
lustrated. i2mo., cloth $2.25 

NYSTROM.— On Technological Education and the Con- 
struction of Ships and Screw Propellers: 

For Naval and Marine Engineers. By John W. Nystrom, 
late Acting Chief Engineer, U. S. N. Second edition, revised, 
with additional matter. Illustrated by seven engravings. 
i2mo $1.00 

O'NEILL. — A Dictionary of Dyeing and Calico Printing: 

Containing a brief account of all the Substances and Processes 
in use in the Art of Dyeing and Printing Textile Fabrics; 
with Practical Receipts and Scientific Information. By 
Charles O'Neill, Analytical Chemist. To which is added 
an Essay on Coal Tar Colors and their application to Dyeing 
and Calico Printing. By A. A. Fesquet, Chemist and En- 
gineer. With an appendix on Dyeing and Calico Printing, 
as shown at the Universal Exposition, Paris, 1867. 8vo. 
491 pages $2.00 

ORTON.— Underground Treasures: 

How and Where to Find Them. A Key for the Ready De- 
termination of all the Useful Minerals within the United 
States. By James Orton, A. M., Late Professor of Natural 
History in Vassar College, N. Y.; author of the "Andes and 
the Amazon," etc. A New Edition, with An Appendix on 
Ore Deposits and Testing Minerals. (1901.) Illustrated. 

$1.50 

OSBORN. — A Practical Manual of Minerals, Mines and 

Mining: 

Comprising the Physical Properties, Geologic Position; 

Local Occurrence and Associations of the Useful Minerals, 



18 HENRY CAREY BAIRD & CO.'S CATALOGUE 

their Methods of Chemical Analysis and Assay; together 
with Various Systems of Excavating and Timbering, Brick 
and Masonry Work, during Driving, Lining, Bracing and 
other Operations, etc. By Prof. H. S. Osborn, LL. D., 
Author of "The Prospector's Field-Book and Guide." 171 
engravings. Second Edition, revised. 8vo $4.50 

OSBORN.— The Prospector's Field Book and Guide: 

In the Search For and the Easy Determination of Ores and 
Other Useful Minerals. By Prof. H. S. Osborn, LL. D. 
Illustrated by 66 Engravings. Eighth Edition. Revised 
and Enlarged. 401 pages. i2mo. (1910.) $1.50 

OVERMAN.— The Moulder's and Founder's Pocket Guide: 

A Treatise on Moulding and Founding in Green-sand, Dry- 
sand, Loam, and Cement; the Moulding of Machine Frames, 
Mill-gear, Hollow Ware, Ornaments, Trinkets, Bells, and 
Statues; Description of Moulds for Iron, Bronze, Brass, and 
other Metals; Plaster of Paris, Sulphur, Wax, etc.; the Con- 
struction of Melting Furnaces, the Melting and Founding of 
Metals; the Composition of Alloys and their Nature, etc., etc. 
By Frederick Overman, M. E. A new Edition, to which is 
added a Supplement on Statuary and Ornamental Moulding, 
Ordnance, Malleable Iron Castings, etc. By A. A. Fesquet, 
Chemist and Engineer. Illustrated by 44 engravings. i2mo. 

$2.00 

PAINTER, GILDER, AND VARNISHER'S COMPANION: 

Comprising the Manufacture and Test of Pigments, the Arts 
of Painting, Graining, Marbling, Staining, Sign-writing, 
Varnishing, Glass-staining, and Gilding on Glass; together 
with Coach Painting and Varnishing, and the Principles of 
the Harmony and Contrast of Colors. Twenty-seventh 
Edition. Revised, Enlarged, and in great part Rewritten. 
By William T. Brannt, Editor of "Varnishes, Lacquers, 
Printing Inks and Sealing Waxes." Illustrated. 395 pp. 
l2mo $1.50 

PERCY.— The Manufacturing of 1 Russian Sheet-Iron: 

By John Percy, M. D., F. R. S. Paper 25 

POSSELT— Cotton Manufacturing: 

Part I. Dealing with the Fibre, Ginning, Mixing, Picking, 
Scutching and Carding. By E. A. Posselt. 104 illustra- 
tions, 190 pp $3.00 

Part II. Combing, Drawing, Roller Covering and Fly Frame, 

$3-oo 

POSSELT.— The Jacquard Machine Analysed and Ex- 
plained : 

With an Appendix on the Preparation of Jacquard Cards, and 
Practical Hints to Learners of Jacquard Designing. By E. A. 



HENRY CAREY BAIRD & CO.'S CATALOGUE 19 

Posselt. With 230 illustrations and numerous diagrams. 
127 pp. 4to $3.00 

POSSELT. — Recent Improvements in Textile Machinery 
Relating to Weaving: 

Giving the Most Modern Points on the Construction of all 
Kinds of Looms, Warpers, Beamers, Slashers, Winders, 
Spoolers, Reeds, Temples, Shuttles, Bobbins, Heddles, Heddle 
Frames, Pickers, Jacquards, Card Stampers, Etc., Etc. By 
E. A. Posselt. 4to. Part I, 600 ills.; Part II, 600 ills. 
Each part $3.00 

POSSELT. — Recent Improvements in Textile Machinery, 
Part III: 

Processes Required for Converting Wool, Cotton, Silk, from 
Fibre to Finished Fabric, Covering both Woven and Knit 
Goods; Construction of the most Modern Improvements in 
Preparatory Machinery, Carding, Combing, Drawing, and 
Spinning Machinery, Winding, Warping, Slashing Machinery, 
Looms, Machinery for Knit Goods, Dye Stuffs, Chemicals, 
Soaps, Latest Improved Accessories Relating to Construc- 
tion and Equipment of Modern Textile Manufacturing Plants. 
By E. A. Posselt. Completely Illustrated. 4to $7.50 

POSSELT.— Technology of Textile Design: 

The Most Complete Treatise on the Construction and Appli- 
cation of Weaves for all Textile Fabrics and the Analysis of 
Cloth. By E. A. Posselt. 1,500 illustrations. 41.0.... $5.00 

POSSELT.— Textile Calculations: 

A Guide to Calculations Relating to the Manufacture of all 
Kinds of Yarns and Fabrics, the Analysis of Cloth, Speed, 
Power and Belt Calculations. By E. A. Posselt. Illus- 
trated. 4to $2.00 

REGNAULT.— Elements of Chemistry: 

By M. V. Regnault. Translated from the French by T. 
Forrest Betton, M.D., and edited, with Notes, by James 
C. Booth, Melter and Refiner U. S. Mint, and William L. 
Faber, Metallurgist and Mining Engineer. Illustrated by 
nearly 700 wood-engravings. Comprising nearly 1,500 pages. 
In two volumes, 8vo., cloth $5.00 

RICH . —Artistic Horse- Shoeing : 

A Practical and Scientific Treatise, giving Improved Methods 
of Shoeing, with Special Directions for Shaping Shoes to Cure 
Different Diseases of the Foot, and for the Correction of 
Faulty Action in Trotters. By George E. Rich. 362 Illus- 
trations. 217 pages. i2mo $2.00 

RICHARDS.— Aluminium: 

Its History, Occurrence, Properties, Metallurgy and Applica- 
tions including its Alloys. By Joseph W. Richards, A. C, 



20 HENRY CAREY BAIRD & CO.'S CATALOGUE 

Chemist and Practical Metallurgist, Member of the Deutsche 
Chemische Gesellschaft. Illust. Third edition, enlarged 
and revised (1895) $6.00 

RICHARDSON.— Practical Blacksmithing : 

A Collection of Articles Contributed at Different Times by 
Skilled Workmen to the columns of "The Blacksmith and 
Wheelwright," and Covering nearly the Whole Range of 
Blacksmithing, from the Simplest Job of Work to some of the 
most Complex Forgings. Compiled and Edited by M. T. 
Richardson. 

Vol. I. 210 Illustrations. 224 pages. i2mo $1.00 

Vol. II. 230 Illustrations. 262 pages. i2mo $1.00 

Vol. III. 390 Illustrations. 307 pages. i2mo $1.00 

Vol. IV. 226 Illustrations. 276 pages. i2mo $1.00 

RICHARDSON.— Practical Carriage Building: 

Comprising Numerous Short Practical Articles upon Carriage 
and Wagon Woodwork; Plans for Factories; Shop and Bench 
Tools; Convenient Appliances for Repair Work; Methods of 
Working; Peculiarities of Bent Timber; Construction of 
Carriage Parts; Repairing Wheels; Forms of Tenons and Mor 
tises; Together with a Variety of Useful Hints and Sugges- 
tions to Woodworkers. Compiled by M. T. Richardson. 

Vol. I. 228 Illustrations. 222 pages. . $1.00 

Vol. II. 283 Illustrations. 280 pages $1.00 

RICHARDSON.— The Practical Horseshoer: 

Being a Collection of Articles on Horseshoeing in all its 
Branches which have appeared from time to time in the col- 
umns of "The Blacksmith and Wheelwright," etc. Com- 
piled and edited by M. T. Richardson. 174. Illustrations, 

$1.00 

RIFFAULT, VERGNAUD, and TOUSSAINT .— A Practical 
Treatise on the Manufacture of Colors for Painting: 

Comprising the Origin, Definition, and Classification of Colors, 
the Treatment of the Raw Materials; the best Formulae and the 
Newest Processes for the Preparation of every description «of 
Pigment, and the Necessary Apparatus and Directions for 
its use; Dryers; the Testing, Application, and Qualities of 
Paints, etc., etc. By MM. Riffault, Vergnaud, and 
Toussant. Revised and Edited by M. F. Malpeyre. 
Translated from the French by A. A. Fesquet. Illustrated 
by Eighty Engravings. 659 pp. 8 vo $5.00 

ROPER. — Catechism for Steam Engineers and Elec- 
tricians : 

Including the Construction and Management of Steam En- 
gines, Steam Boilers and Electric Plants. By Stephen 
Roper. Twenty-first edition, rewritten and greatly enlarged 
by E. R. Keller and C. W. Pike. 365 pages. Illustrations. 
i8mo., tucks, gilt $2.00 



HENRY CAREY BAIRD & CO.'S CATALOGUE 21 



ROPER.— Engineer's Handy Book: 

Containing Facts, Formulae, Tables and Questions on Power, 
its Generation, Transmission and Measurement; Heat, Fuel,' 
and Steam; The Steam Boiler and Accessories; Steam Engines 
and their Parts; Steam Engine Indicator; Gas and Gasoline 
Engines; Materials; their Properties and Strength; Together 
with a Discussion of the Fundamental Experiments in Elec- 
tricity, and an Explanation of Dynamos, Motors, Batteries, 
etc., and Rules for Calculating Sizes of Wires. By Stephen 
Roper. 15th edition. Revised and enlarged by E R 
Keller, M. E„ and C. W. Pike, B. S. With numerous 
illustrations. Pocket-book form. Feather fe.50 

ROPER.— Hand-Book of Land and Marine Engines: 

Including the Modeling, Construction, Running, and Manage- 
ment of Land and Marine Engines "and Boilers. With illu- 
strations. By Stephen Roper, Engineer. Sixth edition. 
i2mo., tucks, gilt edge $3.50 

ROPER.— Hand-Book of the Locomotive: 

Including the Construction of Engines and Boilers, and the 
Construction, Management, and Running of Locomotives 
By Stephen Roper. Eleventh edition. i8mo., tucks gilt 
ed S e $2.50 

ROPER.— Hand-Book of Modern Steam Fire-Engines : 

With illustrations. By Stephen Roper, Engineer. Fourth 
edition, i2mo., tucks, gilt edge fe.50 

ROPER.— Instructions and Suggestions for Engineers and 
Firemen : 
By Stephen Roper, Engineer. i8mo., Morocco $2.00 

ROPER. — Questions and Answers for Stationary and 
Marine Engineers and Electricians: 

With a Chapter of What to Do in Case of Accidents. By 
Stephen Roper, Engineer. Sixth edition, Rewritten and 
Greatly Enlarged by Edwin R. Keller, M. E., and Clayton 
W. Pike, B. A. 306 pp. Morocco, pocketbook form, gilt 
edges •. $ 2-0o 

ROPER. — The Steam Boiler: Its Care and Management: 

By Stephen Roper, Engineer. i2mo., tuck, gilt edges. $2.00 

ROPER.— Use and Abuse of the Steam Boiler: 

By Stephen Roper, Engineer. Ninth Edition, with illus- 
trations. i8mo., tucks, gilt edge $2.00 

ROPER.— The Young Engineer's Own Book: 

Containing an Explanation of the Principle and Theories on 
which the Steam Engine as a Prime Mover is based. By 
Stephen Roper, Engineer. 160 Illustrations, 363 pages. 
l8mo., tuck 52.50 



22 HENRY CAREY BAIRD & CO.'S CATALOGUE 

ROSE.— The Complete Practical Machinist: 

Embracing Lathe Work, Vise Work, Drills and Drilling, Taps 
and Dies, Hardening and Tempering, the Making and Use of 
Tools, Tool Grinding, Marking out work, Machine Tools, etc. 
By Joshua Rose. 395 Engravings. Nineteenth Edition, 
greatly Enlarged with New and Valuable Matter. i2mo., 
504 pages $2.50 

ROSE.— Mechanical Drawing Self -Taught: 

Comprising Instructions in the Selection and Preparation of 
Drawing Instruments, Elementary Instruction in practical 
Mechanical Drawing, together with Examples in Simple 
Geometry and Elementary Mechanism, including Screw 
Threads, Gear Wheels, Mechanical Motions, Engines and 
Boilers. By Joshua Rose, M. E. Illustrated by 330 en- 
gravings. 8vo. 313 pages $3.50 

ROSE.— The Slide-Valve Practically Explained: 

Embracing simple and complete Practical Demonstrations of 
the operation of each element in a Slide-valve Movement, 
and illustrating the effects of Variations in their Proportions 
by examples carefully selected from the most recent and 
successful practice. By Joshua Rose, M. E. Illustrated 
by 35 engravings $1 .00 

ROSE.— Steam Boilers: 

A Practical Treatise on Boiler Construction and Examination, 
for the Use of Practical Boiler Makers, Boiler Users, and In- 
spectors; and embracing in plain figures all the calculations 
necessary in Designing or Classifying Steam Boilers. By 
Joshua Rose, M. E. Illustrated by 73 engravings. 250 
pages. 8vo $2.00 

ROSS. — The Blowpipe in Chemistry, Mineralogy and 
Geology: 

Containing all Known Methods of Anhydrous Analysis, many 
Working Examples, and Instructions for Making Apparatus. 
By Lieut. Colonel W. A. Ross, R. A., F. G. S. With 120 
Illustrations. i2mo $2.00 

SCHRIBER.— The Complete Carriage and Wagon Painter: 

A Concise Compendiun of the Art of Painting Carriages, 
Wagons, and Sleighs, embracing Full Directions in all the 
Various Branches, including Lettering, Scrolling, Ornamenting, 
Striping, Varnishing, and Coloring, with numerous Recipes 
for Mixing Colors. 73 illustrations. 177 pp. i2mo. . .$1.00 

SHAW.— Civil Architecture: 

Being a Complete Theoretical and Practical System of Build- 
ng, containing the Fundamental Principles of the Art. By 
Edward Shaw, Architect. To which is added a Treatise on 



HENRY CAREY BAIRD & CO.'S CATALOGUE 23 

Gothic Architecture, etc. By Thomas W. Silloway and 
George M. Harding, Architects. The whole illustrated by 
102 quarto plates finely engraved on copper. Eleventh edi- 
tion. 4to $5.00 

SHERRATT.— The Elements of Hand-Railing: 

Simplified and Explained in Concise Problems that are Easily 
Understood. The whole illustrated with Thirty-eight Ac- 
curate and Original Plates, Founded on Geometrical Principles, 
and showing how to Make Rail Without Centre Joints, Making 
Better Rail of the Same Material, with Half the Labor, and 
Showing How to Lay Out Stairs of all Kinds. By R. J. 
Sherratt. Folio $2.50 

SHUNK. — A Practical Treatise on Railway Curves and 
Location, for Young Engineers: 

By W. F. Shunk, C. E. i2mo. Full bound pocket-book 
form $ 2 . 00 

SLOANE. — Home Experiments in Science: 

By T. O'Conor Sloane, E. M., A. M., Ph.D. Illustrated by 
91 engravings. i2mo $ T ,oo 

SLOAN. — Homestead Architecture: 

Containing Forty Designs for Villas, Cottages, and Farm- 
houses, with Essays on Style, Construction, Landscape Gar- 
dening, Furniture, etc., etc. Illustrated by upwards of 200 
engravings. By Samuel Sloan, Architect. 8vo $2.00 

SMITH.— The Dyer's Instructor: 

Comprising Practical Instructions in the Art of Dyeing Silk 
Cotton, Wool, and Worsted, and Woolen Goods; containing 
nearly 800 Receipts. To which is added a Treatise on the 
Art of Padding; and the Printing of Silk Warps, Skeins, and 
Handkerchiefs, and the various Mordants and Colors for 
the different styles of such work. By David Smith, Pattern 
Dyer. i2mo \..$i.oo 

SMITH.— A Manual of Political Economy: 

By E. Peshine Smith. A New Edition, to which is added a 
full Index. i2mo $1 2 s 

SMITH.— Parks and Pleasure-Grounds: 

Or Practical Notes on Country Residences, Villas, Public 
Parks, and Gardens. By Charles H. J. Smith, Landscape 
Gardener and Garden Architect, etc., etc. i2mo $2.00 

SNIVELY.— The Elements of Systematic Qualitative 
Chemical Analysis: 

A Hand-book for Beginners. By John H. Snively Phr D 

l6mo '..J2.00 



24 HENRY CAREY BAIRD & CO.'S CATALOGUE 

STOKES.— The Cabinet Maker and Upholsterer's Com- 
panion: 

Comprising the Art of Drawing, as applicable to Cabinet 
Work; Veneering, Inlaying, and Buhl-Work; the Art of Dye- 
ing and Staining Wood, Ivory, Bone, Tortoise-Shell, etc. 
Directions for Lacquering, Japanning, and Varnishing; to 
make French Polish, Glues, Cements, and Compositions; 
with numerous Receipts, useful to workmen generally. By 
J. Stokes. Illustrated. A New Edition, with an Appendix 
upon French Polishing, Staining, Imitating, Varnishing, etc., 
etc. i2mo $1.25 

STRENGTH AND OTHER PROPERTIES OF METALS: 

Reports of Experiments on the Strength and other Properties 
of Metals for Cannon. With a Description of the Machines 
for Testing Metals, and of the Classification of Cannon in 
service. By Officers of the Ordnance Department, U. S. 
Army. By authority of the Secretary of War. Illustrated 
by 25 large steel plates. Quarto $3-00 

SULZ. — A Treatise on Beverages: 

Or the Complete Practical Bottler. Full Instructions for 
Laboratory Work with Original Practical Recipes for all 
kinds of Carbonated Drinks, Mineral Waters, Flavoring 
Extracts, Syrups, etc. By Charles Herman Sulz, Technical 
Chemist and Practical Bottler. Illustrated by 428 Engrav- 
ings. 818 pp. 8vo $7.50 

SYME. — Outlines of an Industrial Science: 

'By David Syme. i2mo , $2.00 

TABLES SHOWING THE WEIGHT OF ROUND, SQUARE 
AND FLAT BAR IRON, STEEL, ETC. 

By Measurement. Cloth 63 

TEMPLETON.— The Practical Examinator on Steam and 
the Steam-Engine. 

With Instructive References relative thereto, arranged for 
the Use of Engineers, Students, and others. By William 
Templeton, Engineer. i2mo $1.00 

THALLNER.— Tool-Steel: 

A Concise Hand-book on Tool-Steel in General. Its Treat- 
ment in the Operations of Forging, Annealing, Hardening, 
Tempering, etc., and the Appliances Therefor. By Otto 
Thallner, Manager in Chief of the Tool-Steel Works, Bis- 
marckhiitte, Germany. From the German by William T. 
Brannt. Illustrated by 69 engravings. 194 pages. 8vo. 
1902 $2.00 

THAUSING.— The Theory and Practice of the Preparation 
of Malt and the Fabrication of Beer: 

With especial reference to the Vienna Process of Brewing. 



HENRY CAREY BAI RD & CO.'S CATALOGUE 25 

Elaborated from personal experience by Julius E. Thausing, 
Professor at the School for Brewers, and at the Agricultural 
Institute, Modling, near Vienna. Translated from the Ger- 
man by William T. Brannt. Thoroughly and elaborately 
edited, with much American matter, and according to the 
latest and most Scientific Practice, by A. Schwarz and Dr. 
A. H. Bauer. Illustrated by 140 Engravings. 8vo 815 
P a § es $10.00 

TOMPKINS.— Cotton and Cotton Oil: 

Cotton: Planting, Cultivating, Harvesting and Preparation 
for Market. Cotton Seed Oil Mills: Organization, Construc- 
tion and Operation. Cattle Feeding: Production of Beef 
and Dairy Products, Cotton Seed Meal and Hulls as Stock 
Feed. Fertilizers: Manufacture, Manipulation and Uses. 
By D. A. Tompkins. 8vo. 494 pp. Illustrated $7.50 

TOMPKINS.— Cotton Mill, Commercial Features: 

A Text-Book for the Use of Textile Schools and Investors 
With Tables showing Cost of Machinery and Equipments 
for Mills making Cotton Yarns and Plain Cotton Cloths. By 
D.A.Tompkins. 8vo. 240 pp. Illustrated $5.00. 

TOMPKINS.— Cotton Mill Processes and Calculations: 

An Elementary Text-Book for the Use of Textile Schools and 
for Home Study. By D. A. Tompkins. 312 pp. 8vo 
Illustrated $ 5 00 

TURNER'S (THE) COMPANION: 

Containing Instructions in Concentric, Elliptic, and Eccen- 
tric Turning; also various Plates of Chucks, Tools, and In- 
struments; and Directions for using the Eccentric Cutter 
Drill, Vertical Cutter, and Circular Rest; with Patterns and 
Instructions for working them. i2mo $1.00 

VAN CLEVE.— The English and American Mechanic: 

Comprising a Collection of Over Three Thousand Receipts, 
Rules, and Tables, designed for the Use of every Mechanic 
and Manufacturer. By B. Frank Van Cleve. Illustrated 
500 pp. i2mo $ 2 0( ; 

VAN DER BURG.-School of Painting for the Imitation 
of Woods and Marbles: 

A Complete, Practical Treatise on the Art and Craft of Grain- 
ing and Marbling with the Tools and Appliances. 16 plates 
Folio, 12x20 inches $6 00' 

VILLE.— The School of Chemical Manures: 

Or, Elementary Principles in the Use of Fertilizing Agents 
From the French of M. Geo. Ville, by A. A Fesquet' 
Chemist and Engineer. With Illustrations. i2mo $1 25 



26 HENRY CAREY BAIRD & CO.'S CATALOGUE 

VOGDES.— The Architect's and Builder's Pocket-Com- 
panion and Price-Book: 

Consisting of a Short but Comprehensive Epitome of Deci- 
mals, Duodecimals, Geometry and Mensuration; with Tables 
of United States Measures, Sizes, Weights, Strengths, etc., of 
Iron, Wood, Stone, Brick, Cement and Concretes, Quanti- 
ties of Materials in given Sizes and Dimensions of Wood, 
Brick and Stone; and full and complete Bills of Prices for 
Carpenter's Work and Painting; also, Rules for Computing 
and Valuing Brick and Brick Work, Stone Work, Painting, 
Plastering, with a Vocabulary of Technical Terms, etc. By 
Frank W Vogdes, Architect, Indianapolis, Ind. Enlarged, 
revised, and corrected. In one volume, 368 pages, full-bound, 

pocketbook form, gilt edges $2.00 

Cloth $1.50 

WAHNSCHAFFE.— A Guide to the Scientific Examina- 
tion of Soils: 

Comprising Select Methods of Mechanical and Chemical 
Analysis and Physical Investigation. Translated from the 
German of Dr. F. Wahnschaffe. With additions by Wil- 
liam T. Brannt. Illustrated by 25 engravings. i2mo. 
177 pages $1.50 

WARE.— The Sugar Beet: 

Including a History of the Beet Sugar Industry in Europe, 
Varieties of the Sugar Beet, Examination, Soils, Tillage, 
Seeds and Sowing, Yield and Cost of Cultivation, Harvesting, 
Transportation, Conservation, Feeding Qualities of the Beet 
and of the Pulp, etc. By Lewis S. Ware, C. E., M. E. 
Illustrated by ninety engravings. 8vo $2.00 

WARN.— The Sheet-Metal Worker's Instructor: 

For Zinc, Sheet-Iron, Copper, and Tin-Plate Workers, etc. 
Containing a selection of Geometrical Problems; also, Prac- 
tical and Simple Rules for Describing the various Patterns 
required in the different branches of the above Trades. By 
Reuben H. Warn, Practical Tin-Plate Worker. To which is 
added an Appendix, containing Instructions for Boiler-Mak- 
ing, Mensuration of Surfaces and Solids, Rules for Cal- 
culating the Weights of different Figures of Iron and Steel, 
Tables of the Weights of Iron, Steel, etc. Illustrated by 
thirty-two Plates and thirty-seven Wood Engravings. 8vo. 

$2.00 

WARNER. — New Theorems, Tables, and Diagrams, for 
the Computation of Earth-work: 

Designed for the use of Engineers in Preliminary and Final 
Estimates, of Students in Engineering and of Contractors 
and other non-professional Computers. In two parts, with 
an Appendix. Part I. A Practical Treatise; Part II. A 



HENRY CAREY BAIRD & CO.'S CATALOGUE 27 

Theoretical Treatise, and the Appendix Containing Notes to 
the Rules and Examples of Part I.; Explanations of the Con- 
struction of Scales, Tables, and Diagrams, and a Treatise 
upon Equivalent Square Bases and Equivalent Level Heights. 
By John Warner, A. M., Mining and Mechanical Engineer. 
Illustrated by 14 Plates. 8vo $3.00 

WATSON.— A Manual of the Hand-Lathe: 

Comprising Concise Directions for Working Metals of all 
kinds, Ivory, Bone, and Precious Woods; Dyeing, Coloring, 
and French Polishing; Inlaying by Veneers, and various 
methods practised to produce Elaborate work with dispatch, 
and at Small Expense. By Egbert P. Watson, Author of 
"The Modern Practice of American Machinists and En- 
gineers." Illustrated by 78 engravings $1.00 

WATSON. — The Modern Practice of American Machinists 
and Engineers: 

Including the Construction, Application, and Use of Drills, 
Lathe Tools, Cutters for Boring Cylinders, and Hollow-work 
generally, with the most economical Speed for the same; the 
Results verified by Actual Practice at the Lathe, the Vise, 
and on the floor. Together with Workshop Management, 
Economy of Manufacture, the Steam Engine, Boilers, Gears, 
Belting, etc., etc. By Egbert P. Watson. Illustrated by 
eighty-six engravings. i2mo $2.00 

WEATHERLY.— Treatise on the Art of Boiling Sugar, 
Crystallizing, Lozenge-making, Comfits, Gum Goods: 

And other processes for Confectionery, including Methods 
for Manufacturing every Description of Raw and Refined 
Sugar Goods. A New and Enlarged Edition, with an Appen- 
dix on Cocoa, Chocolate, Chocolate Confections, etc. 196 
pages. i2mo. (1903.) $1.50 

WILL. — Tables of Qualitative Chemical Analysis: 

With an Introductory Chapter on the Course of Analysis. 
By Professor Heinrich Will, of Giessen, Germany. Third 
American, from the eleventh German edition. Edited by 
Charles F. Himes, Ph. D., Professor of Natural Science, 
Dickinson College, Carlisle, Pa. 8vo $1.00 

WILLIAMS.— On Heat and Steam: 

Embracing New Views of Vaporization, Condensation and 
Explosion. By Charles Wye Williams, A. I. C. E. Illus- 
trated. 8vo | 2 00 

WILSON.— The Practical Tool-Maker and Designer: 

A Treatise upon the Designing of Tools and Fixtures for 
Machine Tools and Metal Working Machinery, Comprising 
Modern Examples of Machines with Fundamental Designs 



2« HENRY CAREY BAIRD & CO.'S CATALOGUE 

for Tools for the Actual Production of the work; Together 
with Special Reference to a Set of Tools for Machining the 
Various Parts of a Bicycle. Illustrated by 189 engravings 

(1898.) : $2.50 

CONTENTS: Introductory. Chapter I. Modern Tool Room and 
Equipment. II. Files, Their Use and Abuse. III. Steel and Tempering. 
IV. Making Jigs. V. Milling Machine Fixtures. VI. Tools and Fixtures 
for Screw Machines. VII. Broaching. VIII. Punches and Dies for Cut- 
ting and Drop Press. IX. Tools for Hollow- Ware. X. Embossing: Metal. 
Coin, and Stamped Sheet-Metal Ornaments. XI. Drop Forging. XII. 
Solid Drawn Shells or Ferrules; Cupping or Cutting, and Drawing; Break- 
ing Down Shells. XIII. Annealing, Pickling, and Cleaning. XIV. Tools 
for Draw Bench. XV. Cutting and Assembling Pieces by Means of Rat- 
chet Dial Plates at One Operation. XVI. The Header. XVII. Tools for 
Fox Lathe. XVIII. Suggestions for a set of Tools for Machining the 
Various Parts of a Bicycle. XIX. The Plater's Dynamo. XX. Conclu- 
sion — With a Few Random Ideas. Appendix. Index. 



BRANNT'S "SOAP MAKER'S HAND BOOK." 



The most helpful and up-to-date book on the Art of Soap 
Making in the English language. 

In one volume , 8vo, 535 pages, illustrated by 54: engravings. 
Price $6.00 net. Free of Postage to any Address in the World, 
or by Express C O. D. freight paid to any Address in the 
United States or Canada. 



PUBLISHED APRIL, 1912. 



THE 

SOAP MAKER'S HAND BOOK 

OF 

MATERIALS, PROCESSES AND RECEIPTS FOR 
EVERY DESCRIPTION OF SOAP 

INCLUDING 

FATS, FAT OILS, AND FATTY ACIDS ; EXAMINATION OF FATS AND OILS ; 

ALKALIES ; TESTING SODA AND POTASH ; MACHINES AND UTENSILS J 

HARD SOAPS ; SOFT SOAPS ; TEXTILE SOAPS ; WASHING POWDERS 

AND ALLIED PRODUCTS ; TOILET SOAPS, MEDICATED SOAPS, 

AND SOAP SPECIALTIES ; ESSENTIAL OILS AND OTHER 

PERFUMING MATERIALS ; TESTING SOAPS. 

EDITED CHIEFLY FROM THE GERMAN OF 
DR. C. DEITE, A. ENGELHARDT, F. WILTNER, 

AND NUMEROUS OTHER EXPERTS. 

WITH ADDITIONS 
BY 

WILLIAM T. BRANNT, 

EDITOR OF "THE TECHNO CHEMICAL RECEIPT BOOK." 

ILLUSTRATED BY FIFTY-FOUR ENGRAVINGS. 
SECOND EDITION. REVISED AND IN GREAT PART RE-WRITTEN. 



PHILADELPHIA : 

HENRY CAREY BAIRD & CO., 

INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS, 

810 Walnut Street. 

1911 



KIRKS CUPOLA FURNACE. 



An Eminently, Practical, Up-to-Date Book, by an Expert. 

Third Thoroughly Revised and Partly Re-written Edition. 
In one volume, 8vo., 482 pages, illustrated by one hundred 
and six engravings. Price $3.50. Free of Postage to any 
Address in the World, or by Express C. O. D., freight paid to 
any Address in the United States or Canada. 



PUBLISHED AUGUST, 1910. 



THE CUPOLA FURNACE 

A PRACTICAL TREATISE ON THE 

CONSTRUCTION AND MANAGEMENT 

OF 

FOUNDRY CUPOLAS: 

COMPRISING 

IMPROVEMENTS IN CUPOLAS AND METHODS OF THEIR CONSTRUCTION AND MANAGE- 

MENT; TUYERES; MODERN CUPOLAS; CUPOLA FUELS; FLUXING OF IRON; GETTING 

UP CUPOLA STOCK; RUNNING A CONTINUOUS STREAM; SCIENTIFICALLY 

DESIGNED CUPOLAS; SPARK-CATCHING DEVICES; BLAST-PIPES AND 

BLAST; BLOWERS; FOUNDRY TRAM RAIL, ETC., ETC. 

BY 

EDWARD KIRK, 

PRACTICAL MOULDER AND MELTER, CONSULTING EXPERT IN MELTING. 

Author of " The Founding of Metals ," and of Numerou: Papers on Cupola Practice. 

ILLUSTRATED BY ONE HUNDRED AND SIX ENGRAVINGS. 

THIRD THOROUGHLY REVISED AND PARTLY RE-WR.TTEN EDITION. 



PHILADELPHIA : 

HENRY CAR2Y BAIRD & CO., 

INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS, 
810 Walnut Street. 



KIRK'S FOUNDRY IRONS. 



A Practical, Up~£o-Date Book, by the well known Expert, 
In one volume, 8vo, 294 pages, illustrated. Price $3.00 net. 
Free of Postage to any Address in the World, or by Express 
C. O. D., freight paid to any Address in the United States or 
Canada. * 



PUBLISHED JUNE, 1911. 



A PRACTICAL TREATISE 



ON 

FOUNDRY IRONS: 

COMPRISING 

PIG IRON, AND FRACTURE GRADING OF PIG AND SCRAP IRONS ; 
SCRAP IRONS ; MIXING IRONS ; ELEMENTS AND METALLOIDS ; 
GRADING IRON BY ANALYSIS ; CHEMICAL STANDARDS 
FOR IRON CASTINGS ; TESTING CAST IRON ; SEMI- 
STEEL ; MALLEABLE IRON ; ETC., ETC. 



BY 

EDWARD KIRK, 

PRACTICAL MOULDER AND MELTER ; CONSULTING EXPERT IN MELTING. 

AUTHOR OF "THE CUPOLA FURNACE," AND OF NUMEROUS 

PAPERS ON CUPOLA PRACTICE. 



ILLUSTRATED 



PHILADELPHIA : 

HENRY CAREY BAIRD & CO., 

INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS, 

810 Walnut Street. 

1911 



BRANNT'S DRY CLEANER. 



The only book including Hat Cleaning and Reno- 
vating in any language, in one volume, 12mo, 371 
pages, illustrated. Price $2.50 net. Free of postage 
to any address in the world, or by express freight 
paid to any address in the United States or Canada. 



PUBLISHED OCTCEER, 1911. 



THE PRACTICAL 

DRY CLEANER, SCOURER, AND 
GARMENT DYER : 

COMPRISING 

DRY, CHEMICAL, OR FRENCH CLEANING; PURIFICATION OF BENZINE; 

REMOVAL OF STAINS, OR SPOTTING; WET CLEANING; FINISHING 

CLEANED FABRICS; CLEANING AND DYEING FURS, SKIN RUGS 

AND MATS; CLEANING AND DYEING FEATHERS; CLEANING 

AND RENOVATING FELT, STRAW AND PANAMA HATS; 

BLEACHING AND DYEING STRAW AND STRAW HATS; 

CLEANING AND DYEING GLOVES; GARMENT 

DYEING; STRIPPING; ANALYSIS OF 

TEXTILE FABRICS. 

EDITED BY 

WILLIAM T. BRANNT, 

EDITOR OF "THE TECHNO-CHEMICAL RECEIPT BOOK." 

FOURTH EDITION, REVISED AND ENLARGED. 
ILLUSTRATED BY FORTY-ONE ENGRAVINGS. 

PHILADELPHIA: 

HENRY CAREY BAIRD & CO., 

INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS, 

810 WALNUT STREET. 

1911. 



OCT 27 1913 



